Clear Voice DENOISER Automatic Noise Cancellation software USER'S GUIDE

Voice of the Future

Speech Technology Center

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Clear Voice Denoiser User’s Guide Speech Technology Center Saint Petersburg, Russia

Copyright Copyright © 1999, 2000 by Speech Technology Center Limited (STC Ltd.). All rights reserved. Clear Voice Denoiser in a part or as a whole may be used according to the corresponding license. To receive more copies or other information, please contact STC.

Disclaimer Speech Technology Center accepts no liability whatsoever for any loss or injury incurred by the owner or by any third party while using this Clear Voice Denoiser and specifically disclaims any warranties, merchantability or fitness for any particular purpose. The contents of the Clear Voice Denoiser and User’s Guide are subject to change without notice.

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Contents

CONTENTS .................................................................................................................................................................5

PREFACE.....................................................................................................................................................................7 CLEAR VOICE FAMILY PRODUCTS.......................................................................................................................... 7 CLEAR VOICE DENOISER ALGORITHM .................................................................................................................. 8

CLEAR VOICE DENOISER SOFTWARE........................................................................................................9 HOW TO USE CLEAR VOICE DENOISER SOFTWARE ........................................................................................... 11 CONTROL PANEL TOOLBAR.................................................................................................................................. 12 CHOOSING A SOUND FILE...................................................................................................................................... 13 PROCESSING THE LIST OF SEVERAL SOUND FILES.............................................................................................. 14 SOUND FILE PROCESSING....................................................................................................................................... 17 SOUND PLAYBACK.................................................................................................................................................. 18 WAVEFORM VIEWING............................................................................................................................................ 18

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EDITING OF THE SIGNAL PROCESSING FILTER PARAMETERS.......................................................................... 21 TUNING NOISE REDUCTION DEGREE................................................................................................................... 21 TYPICAL FILTER SETTINGS.................................................................................................................................... 23 MANUAL ADJUSTMENT OF NOISE REDUCTION FILTER..................................................................................... 26 RETURN TO DEFAULT FILTER PERFORMANCE..................................................................................................... 28 OPTIONS................................................................................................................................................................... 28 MUSIC APPLICATIONS............................................................................................................................................ 43

TROUBLESHOOTING..........................................................................................................................................46

USER SUPPORT......................................................................................................................................................49

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Preface

Clear Voice family products STC propose to the users an excellent set of software tools for noise cancellation and signal enhancement for noisy sound files. ClearVoice family products include Denoiser, Denoiser-by-Reference and Declicker. • Denoiser is intended to remove automatically slow varying background noise and partially narrowband noise (bad channel, office and industrial noise, traffic noise, etc.). It is the best means to enhance poor quality speech sound recordings (e.g. real life sound reporting, etc.). • Denoiser-by-Reference is intended to remove automatically with minimal manual control stable background noise and partially narrowband noise (vinyl plates side-effects, tape hiss, etc.). It is the best means to remove background noise in old sound archives. • Declicker is intended to remove automatically clicks (spike-like or pulse-like noise). It is the best means to remove sound sand from recordings in old sound archives. The algorithmes realized in these software titles are also used in STC Sound Cleaner – a universal software for noise cancellation and speech enhancement.

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Clear Voice Denoiser algorithm Clear Voice Denoiser introduces a proprietary, original, state-of-the-art algorithm which is developed to remove background noise automatically from input signals and to enhance the sound quality of speech and other useful transmitted or pre-recorded signals. Denoiser algorithm in difference to other algorithms of Clear Voice package (Denoiser-by-Reference and Declicker) removes from the input signal broadband noise and partially narrowband noise. It dramatically improves communication quality for signal in telephone, satellite and radio channels when noise is present, and can be used to increase the accuracy of speech recognition systems and vocoders. It is effective against a wide variety of noise sources (air conditioner, desk or computer fan, background babble, office equipment, industrial and vehicle engines, street traffic, wind, slow music, power supply hum, communication channels, etc.) Algorithm is intended for both inexperienced amateurs and advanced professionals and is functioning automatically but can be additionally manually adjusted for the very exact correspondence to a specific applied task.

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Clear Voice can be implemented in real-time on embedded chips (customised large-scale ICs, or standard DSP) or can be run on a PC under Windows in order to remove undesirable environment noise from live or pre-recorded voice.

Clear Voice Denoiser software Denoiser Software is a perfect tool to restore noise-corrupted poor quality speech recordings. It reduces slow varying broadband and narrowband noise from processed sound signals. Main features: • Simple and extremely user-friendly interface • Up to 40 dB signal-to-noise improvement • Single tone reduction > 70 dB

10 Figure 1. The working window of Denoiser software.

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• White noise reduction > 20 dB. • Automatic suppression of the majority of the really existing noise types (from 8 up to 60 dB) • Programmable noise reduction parameters for the most fine tuning. This simple and user-friendly software may serve as a powerful tool for sound quality improvement with any kind of background broadband noise and partially narrowband noise. It works in Windows 95, 98, NT environment. For sound playback it can use SoundBlaster compatible soundboards or professional STC sound boards (STC-H118).

How to use Clear Voice Denoiser software If you have sound file with noisy speech or other useful for you signal, you can get this sound file (source file) cleared and have a new sound file with better speech intelligibility after processing by Denoiser software. Firstly, run Denoiser.exe, then you will see the working window of Denoiser software. (If you run the software for the first time you will be asked to enter the registration data).

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Using controls you can choose a sound file, process it, listen to source or processed sound, adjust noise cancellation filter parameters and to see the waveform of the sound signals.

Control Panel toolbar On the top of the working screen you can see the toolbar Control Panel with buttons. Clicking on the corresponding button you can select a required function of the software.

Figure 2. Control panel of Denoiser SDK software.

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Choosing a sound file By this software you can improve speech and other useful signal quality and reduce many types of noise for previously recorded 8/16 bit PCM mono or stereo *.wav sound files. To process a

specific file click on the <Open source file> button in the <Control panel> tool bar. Select the required file name by standard Windows means. In the <Source file > field of the working window you will see the chosen file name. In the field <Target file> in the working window you will see the name of the target sound file with the processed, cleaned signal. The default name will be the name of the chosen source sound file with the adding of signs *_CLR before its file extension. You can change this name and file location typing any new file name with the required path in the <Target file> field. The processed sound file has standard PCM 16 bit Windows *.wav format.

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Processing the list of several sound files

If you would like to process not one but severale sound files, you can use the <Sound list> button. After clicking this button, you will have in the screen an additional working window.

Figure 3. Sound list window.

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In order to choose required sound files to process, you should click <Add> button. You will see the working folder. You should select all necessary files by means of the Windows standard working tools. You can browse various folders and choose there several files into this one working Sound list. After such selection in the <Sound list> window you will have a list of selected files.

Figure 4. Sound list window with a list of choosen files.

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Using standard tools you can select in the list some files and remove them from the list clicking

<Subtract> button.

Figure 5. Sound list window with a list of choosen files. Four of them are selected.

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In order to cancel the noise in several files you can select in the Sound list all required files using <Shift> and <Ctrl> buttons and arrows keys of the keyboard or the left button of the mouse.

Once you have selected a pre-recorded file, click on <Clean> button in this window. After filtering, the processed sound signal for every source one is recorded in a new file with the same name plus additional letters _CLR before the extension. This file is located in the same folder, where the corresponding source file is.

Clicking <Stop> button you can stop processing. After processing, red check sign is situated to the left to the processed file name.

Sound file processing

Once you have opened a pre-recorded file, click on <Clean> button in <Control panel>. After several seconds you will have a processed sound signal of the source file in the target file.

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Clicking <Stop> button you can stop processing. In this case target file contains only a part of the processed file.

Sound playback Play the sound before and after noise reduction. To play the original source sound click on

<Play source> button (a green one) in <Control panel> tool bar.

To listen to the filtered sound after processing, click on <Play target> button (a blue one).

Pressing of <Stop playback> button stops sound playback.

Waveform viewing At the bottom of the working window you can see the waveform pictures of the sound files. Before processing you will see a waveform of the source file (green color).

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After processing you will see over the previous picture a waveform of the processed file (blue color).

Figure 6. Waveform field with a waveform of a source audio signal.

Figure 7. Waveform field with a waveform of a source audio signal (green) and of the processed signal (blue).

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Using the mouse pointer and left mouse button you can select in the waveform field any part of the sound files to listen to. Put the mouse pointer to the place of the desirable beginning of the part to listen to and press the left mouse button. Move the pointer in the required direction holding the mouse button pressed and release it at the palce, where you would like to finish the selection. This selection is showed in the waveform field by two adjustable vertical lines (markers) and by the changed color of the picture between the markers. Clicking by right mouse button on the

Figure 6. Waveform field with waveforms of a source audio signal. The selected part of the signals are shown by reverse colors (gray area).

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waveform field (or on <Selection> button in <Control panel> toolbar) removes selection markers from the waveform field. If you work with <Sound list> of several files, you will have the waveform picture of the given file(s) in the waveform field after clicking twice the desirable file(s) in the list.

Editing of the Signal Processing Filter Parameters Denoiser filter works automatically, but you can adjust filter performance additionally.

Clicking <Exclamation> button or button returns all filter settings to their default values.

Important: We recommend manual adjustment of filter control parameters only to advanced users! There are several ways to change noise suppression filter performance

Tuning Noise Reduction Degree You can adjust Noise reduction degree (or depth), i.e. quantity of the noise to be removed with all other parameters of the algorithm fixed. As speech and noise as usual have some similar

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signal components, sometimes Denoiser filter changes useful signal during noise removal. Not all such changes are acceptable for specific application or situation. So the user should choose a trade-off between the most noise removal and the most natural speech signal.

STC experts chose and set in Standard mode of Denoiser (default state when button at <Mode> panel is pressed) the optimized universal combinations of all control parameters of noise reduction filter. The only control which can be changed in this mode is

<Noise Reduction Degree>. It determines the general noise suppression depth and the level of residual noise. In order to get the best compromise of noise level and speech quality for your noisy sound in the most simple way you can use <Noise Reduction Degree> slider in <Mode> panel. This control works only if <Standard> button is pressed. You can change the slider horizontal position by mouse clicking to the left or to the right of the slider and adjust the total noise reduction degree (depth). The most left position of the slider (value 1) corresponds to the most saved but a bit noisy result. The most right position (value 10) corresponds to the most severe noise suppression but with

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possible loss in the useful signal quality (there may appear music noise). Typical noise suppression for different slider positions and thecorresponding values are the following: 1 - 8dB, 2 - 11dB,3 - 14dB, 4 - 18dB, 5- 21dB, 6 - 24dB, 7 - 27Db, 8-30dB, 9 - 35dB, 10 - 40dB Typically this Noise Reduction Degree slider should be in the center of the control field, and a reasonable noise reduction is 14-23 dB. An acceptable value depends on the type of the sound and even on the used speaker or headphones and the distance between loudspeaker and listener.

Typical filter settings The algorithm adjustment which is more sophisticated but standard for some specific signals can be chosen after adjusting filter settings for several preliminary recorded files of the same

type. Click on <Professional> button in <Mode> panel. After that the Current setting field will be active. Then you can choose some typical options, choosing available ready-made sets of filter settings

from List of the typical filter set-ups. To do it, choose a required set clicking the pointer in

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the right part of this field in <Typical set-ups list> window. You will see the list of available types of settings.

Figure 7. List of typical filter settings.

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Clicking on the required settings name you load those settings into the filter and they are valid until you change filter settings manually or load a new set of filter parameters. In regard to typical available settings we can say that music sound or sound files for acoustical CD with the very high demands on output signal quality usually require different filter adjustment than speech signals for telecommunication tasks. The reason is that in telecommunication applications the main aim of signal processing is the maximal intelligibility improvement, whereas for music and entertainment application the sound naturalness is far more important. For example, for CD mastering sometimes CD quality 01 settings provides the user with a bit better noise reduction and more gentle processing of the useful signal for files with 44100Hz sampling rate. The same settings for speech signal at 8000Hz sampling rate and telecommunication sound quality would provide a small audible echo and not the maximal noise reduction degree.

<Example> button to the right from <Options> button load the sound file with a short sound example, for which the filter settings in the chosen set are the most reasonable. These example files are included only in the full professional delivery set.

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In order to process source sound file with the new options click on <Clean> button in <Control panel>. For noise reduction in Automatic Speech Recognition (ASR) applications we recommend to try the universal settings of <Standard> mode as well some of Automatic speech recognition settings in the list. Usual Universal settings may sometimes provide you with quite good subjective sound quality but at the same time with rather poor performance improvement for a specific ASR engine. The best sound quality for human ear and computer ear are usually rather different. At STC web site you can find and look at a special demonstration kit Demo of Clear Voice for ASR applications. There are sound files and ASR engine which demonstrate methods of Clear Voice technology implementation for ASR tasks.

Manual adjustment of Noise Reduction Filter We recommend to use the manual mode of adjustment only for advanced and fastidious users. You can change the options of the noise canceling filter in Manual mode by clicking on

<Options> button in the toolbar. This button is active only when <Professional> button

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in <Mode> panel is pressed. After pressing <Options> button you will see <Options> window in the upper part of the working window.

Figure 8. Options field.

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In this field you can change any settings by clicking and moving by mouse pointer on controls. Clicking on the <OK> button confirms all new filter settingss and they are set for the current filtration process. In order to process the source sound file with the new filter options click on the <Clean> button in <Control panel> tool bar. Clicking on <Cancel> button restores settings as they were berore entering this field.

Return to default filter performance

Clicking <Defaults> button in <Control panel> tool bar or <Standard> button in <Mode> panel returns all filter settings to their universal standard values.

Options

Figure 9. Advanced settings window.

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<Noise Detail> This feature corresponds to the duration in samples of a piece of the source signal that is used for processing. The bigger is Noise Detail during signal processing, the better is noise reduction. But at the same time bigger Noise detail values can provide with some audible echo effect.

Table 1. Typical & additional Frame size values for various sampling rates of the source signal files

Sampling rate of source sound file in Hz

Standard <Noise Detail> value

Additional <Noise detail> values

8000 Shortened standard Small, Standard 11025 Standard Shortened or Extended standard 16000 Standard Extended standard, Large 22050 Extended standard Extended standard, Large 44100 Large Extended standard,

Extra large In standard mode Noise Detail is set automatically according to the sampling rate of the source signal. There is an approximate correspondence between Noise detail degree and Frame size

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in samples for signal processing: Extra small – 60, small – 130, shortened standard – 260, standard – 500, extended standard – 1000, large – 2000, extra large – 4000.

<Speed of calculation>

Denoiser suppression procedure has two modes of signal processing. The first mode <Best performance mode> has a bit higher output sound quality. Experts can hear a more soft sound for high quality source signals without any artifacts in sounding. The second <Fast> mode is about twice less demanding on calculating power and provides with sufficiently high sound quality for many practical applications, in particular for signals with telecommunication quality of sounding. For fast mode some very soft clicks may sometimes occur, especially in empty frequency bands. This mode may be useful to evaluate the algorithm acceptability in applications with limited calculation recourses.

<Type of sound>

You can choose type of the source signal by putting a dot in the corresponding circle ‘Speech-like’ or ‘Music-like’. The difference in output sounding is not very big, but skilled experts find that for high-quality source signals, especially with background music the <Music> mode is more

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appropriate. At the same time for poor quality and very noisy phone conversations with low sampling rates <Speech> mode provides aurally better sounding. For some noisy speech files with high sampling rate (44100Hz or more) <Music> option provides better sound quality of the output signal.

<Tone correction> This option enables users to realize additional Low pass and High pass frequency filters. Lowpass filtering is the simplest way to reduce or eliminate the low frequency hum, background mumble and babble. Highpass filtering allows to eliminate or reduce harmful hiss or high-tonal squeak and creak. Though the general procedure suppresses low and high frequency components of noise the user sometimes can get improved results while using these features to minimize the impact of noise by means of excluding frequencies containing noise. Using < LF frequency> you can specify frequency of Low pass filter. For lower frequencies the filter envelope has a fast uniform roll-off to 0Hz. Using < HF frequency> you can specify frequency of Highpass filter. For higher frequencies the filter envelope has a fast uniform roll-off to the half of the current sampling rate in Hz.

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The frequency boundaries and amplifying of additional filters should be chosen by ear in accordance with signal quality and type.

Table 2. Typical values of HF and LF parameters.

Type of the sound signal LF frequency in Hz HF frequency in Hz Telephone conversation 200 3400 Tape record 100 4000 – 7000 Dictaphone record 200 3600 CD quality sound 70 10000-15000 Master CD 20 20000

<Power hum reduction> By mouse clicking you can make this filter option active (a tick in the box) or passive (a blank box).

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This algorithm feature is turned on by default Clear Voice settings and corresponds to activation of the additional suppression of narrowband or harmonic (Sin-wave like) components of the hindrances. Without this feature being activated attenuation of the tonal noise components in processed sound is equal to Noise Reduction Depth, which is set by <Noise reduction degree> option in <Mode> panel (typically 17-20 dB). Activating of this feature provides with pure tones attenuation by 50-75 dB. When activated, this option enables the procedure to remove additionally bells, horns, power supply hum, buzz, whistle and similar tonal sounds, being in sound signal to filter. So that Denoiser can reduce significantly these tonal hindrances the frequency and amplitude of their harmonics is to vary relatively slow. The faster tonal hindrances are changing, the less <Adaptation time> parameter should be in <Advanced options> panel. Sometimes such additional tonal sounds components reduction is not desirable, because they may be components of the useful signal (for example, slow music). In this case this option should be turned off. The more <Noise Detail> is, the more effective this option works is and vice versa.

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<Max> This control corresponds to Maximal Noise Suppression Depth (in dB scale), that is limiting threshold for total noise reduction degree. This control determines the minimal possible residual noise level in output signal. It reflects the target improvements in decibels for Signal-to-Noise-Ratio for sound before and after processing. Broadband noise is reducing in the processed source sound signal not more then by this value. This control option is used to reduce the effect of residual disturbances and in particular so called music noise appearance in the output sound signal. If all other options are fixed, then reducing of this parameter increases the level of audible residual noise by 1 dB for 1 unit of parameter change. In other words: noise is to be half as much, if <Max> is increased twice. If <Max>is decreased, then residual background noise is getting audibly more strong, but uniform and homogeneous, in addition output signal has less and less audible artifacts, i.e. short and soft bells and tones, which might be heard in pauses. If <Max>is increased, then residual background noise is getting less audible, but in the same time it is getting less homogeneous and less suitable in aural quality. In extreme cases it may appear audible, so called musical noise - a random combination of short different tones, as if somebody is randomly striking different piano keys. Especially this effect is noticeable in pauses.

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As usual it is reasonable to change this parameter in the range +-3/6 dB from standard value in order to achieve a little more effective noise reduction results. Note, that 6 dB corresponds to the change of noise level in 2 times. Range of <Max> is 0-60. Simultaneously with <Max> should be changed <Suppression> control. Both these options should have got some increasement or some decreasement. It is reasonable to use as a starting point for the choice of the best parameter value, the value in standard mode, which is set when <Default for>, value 4 is pressed.

<Suppression> The meaning of this control corresponds to Strength of noise reduction. This parameter determines the amount of noise, which the filter attempts to eliminate from the processed audio file. The previous control bounds the realization of noise suppression on the level of <Max> value in dB. The more <Suppression> is, the more noise reduction is, but in the same time the more distortions are put into the residual useful sound signal, because weak, noise-like speech components are suppressed, too. The best results are obtained if used noise reduction degree matches the real proportion between undesirable noise and useful signal.

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Denoiser noise reduction algorithm leaves without changes all speech components that are bigger then some threshold and gives quite significant noise reduction for speech components, which have the amplitude level less then this threshold. Current Suppression value determines the location of this threshold. There should be quite strong dependence between this and the previous parameters optimal values. When Suppression is arisen from 1 to 40 in the same time Max should be usually increased, too, from 8 to 50, and vice versa. <Smoothing in frequency> and <Smoothing in time> controls have big influence on real noise reduction intensity, too. It is reasonable to use as a starting point for the choice of the best parameter value, the value in standard mode, which is set when <Default for>, value 4 is pressed.

<Contrast> This parameter determines the difference (that is contrast) in noise reduction degree for loud and soft parts of the processed signal. The more the value of the Contrast parameter is, the more difference between noise reduction degree for soft parts of the input signal in comparison with loud ones is. Typically, Contrast should have maximal value. But lower values could sometimes provide gentler sounding of output signal.

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<Smoothing in frequency> This control determines the smoothness in frequency of the spectrum of output sound signal. This feature is used to reduce the spectral homogeneity of the residual noise. If this parameter is too low, the processed signal will sound a bit rough and mechanical. Sometimes it will be corrupted by a specific disturbance, so called musical noise - a random combination of short different tones, as if somebody is randomly striking different piano keys. If the spectral smoothing is too large, the noise reduction degree is bigger in total, but is less detailed, and the output signal might sound hollow and lifeless. The bigger this parameter is, the less <Max> value should be set. The maximal values of this parameter may be used to reduce the iron in the sounding. Range of changing is 1-40. It is reasonable to use as a starting point for the choice of the best parameter value, the value in standard mode, which is set when <Default for>, value 4 is pressed.

<Smoothing in time> This feature is used to reduce the time uniformity and homogeneity of the residual noise. If this parameter is too low, the processed signal will sound a bit mechanical. Sometimes it will be corrupted by a specific disturbance, so called musical noise - a random combination of short

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different tones, as if somebody is randomly striking different piano keys. If the time smoothing is too large, the noise reduction degree is less and an output signal might sound with a small echo effect. The parameter is useful to decrease the hardness and iron quality in the sound. Range of changing is 0-9. It is reasonable to use as a starting point for the choice of the best parameter value, the value in standard mode, which is set when <Default for>, value 4 is pressed.

<Adaptation time>

This control corresponds to characteristic time of the tuning of the noise reduction filter towards the best noise removal from the source sound signal. Range of changes is between 0.1 and 100 seconds. The faster changing the background noise to remove is, the less this parameter should be. But if the Adaptation time is less than 2 sec, then some speech signal components are removed, too. So for telephone conversation the usual value of this parameter is 2.5-5 seconds. High quality sound with music background demands to increase Adaptation time up to 60 seconds and more.

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<Automatic gain control of output file> The activation of this option allows to save the middle amplitude of the output signal as constant even if an input signal has big changes in its loudness.

<Amplification> This parameter provides additional gain of the output sound signal by given number of decibels (dB). This control is used when the useful signal is much more less than removed noise and after noise cancellation the sounding is too soft. Usual range is equal to 0-20 dB. The standard value of 0 dB produces no increase in voice. 6 dB approximately doubles voice level and 12 dB increases voice level four times. Setting the gain too high can distort the sound. If the sound is distorted, reduce the gain. Also, see How to Set the Output Level.

Noise reduction degree <Default for>

This control allows setting of all the current filter options to their defaults values for Universal mode.

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For this aim in the panel Noise reduction degree set the required value

of the total noise reduction degree by clicking button. If 0, then default parameters set is not used, and all parameters are taken from <Options> panel. If 1-10, all other parameters of this working control panel are set to values, which correspond to default parameters set in Universal mode. The standard value 1 corresponds to minimal noise reduction degree and provides the most saved and natural input signal with typical noise reduction by 8dB. The value 10 provides typical noise reduction by 40 dB but sometimes the output sound signal could have got some smearing, nibbling or other audible corruption. So this general Noise Reduction Degree scale has at the one pole (value 1) ‘The best useful signal quality and small level of noise suppression’ and at the second pole (value 10) ‘A bit corrupted useful signal and very large level of noise suppression’. Recommended default standard value is equal to 3-5.

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Save settings to the file

You can save your own filter options in the new *.set file using button <Save to file> After pressing it you will see the dialog window <Settings file saving>. In dialog box fields you will have information corresponding to the last saved *.set file. Please, type a new file name and a title of your new settings composition. This title will be used in the list of available set-ups after pressing <Professional> button in <Mode> panel.

Figure 10. Dialog box of settings file saving.

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If you want you can save an example of the sound file, which is most suitable for the given filter options set. To do it, type a name of the example file in the third line of the dialog box. When all the fields are filled, press <Save> button. Automatic Speech Recognition applications Clear Voice Denoiser algorithm can be used as a front-end preprocessor of input live sound signal or pre-recorded sound file for applications of automatic speech, speaker or language recognition. In such a case, it can dramatically increase the success rate of any engine working in noisy background. It is important to note that usual Universal noise canceling filter options are, in general, not so good for automatic speech recognition application. Depending on specific front-end ASR procedures using of special filter tuning can sometimes significantly increase the positive effect. It confirms the fact that subjective good speech quality (as perceived by a human ear) is not neccessarily good for a technical application. For such tuning you should use Professional mode of the filter adjustment. Click on

<Professional> button in <Mode> panel. After that list of set-ups will be

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active. Then you should choose an available ready-made set of filter settings from this list by

clicking the pointer in the right part of this display. Clicking the name of a set, you load those settings into the filter and they are valid until you change filter settings manually or load a new set of filter parameters. For ASR we recommend to use ONLY Automatic speech Recognition. Mode XX settings set. You can try to get even better results by slightly changing values of some settings (especially Max, Suppression, Smoothing in frequency and time).

In order to process the source sound file with the new options click <Clean> button in <Control panel>.

Music applications Clear Voice Denoiser algorithm can be successfully used for CD mastering and processing of the relatively high-quality records of music and speech. It is important to note that standard Universal noise canceling filter setting may be, in general, not so good for such tasks. After background noise reduction, there might occur some loss in speech and music quality, appear several slightly heard music noise or echo. Often using special filter tuning can significantly

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increase the output sound quality. Only big experience of practical filter adjustment can help you to find out the filter options with really maximal positive effect and minimal residual noise. For such tuning you should use Professional mode of the filter adjustment. Click <Professional>

button in <Mode> panel. After that the list of set-ups will be active. Then you should choose an available ready-made set of filter settings from this list by clicking the

pointer in the right part of this list. Clicking the name of a set, you load those settings into the filter and they are valid until you change filter settings manually or load a new set of filter parameters. As the first step we recommend to use any of CD quality XX settings sets. You can try to get even better results by slightly changing values of some parameters, especially Adaptation time, Max, Suppression, Smoothing in frequency and time.

In order to process source sound file with the new options click <Clean> button in <Control panel>.

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Specially for more careful sound file processing during noise removal in music applications, STC has a separate product Denoiser by reference.

Figure 11. List of typical filter settings.

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Troubleshooting Little or no sound output Check the level of the input and output sound files in the waveform picture. They are to have non-zero amplitude values. Check the current volume control level at the bottom of the working window of Denoiser

Software . The slider should be at the right side of the scale. See How to Set the Output Level. Make sure the speaker or line-out cable is plugged into the correct output on your sound board. Check that the speaker has electrical power and that the switch is turn on. How to Set the Output Level. If the sound level is too low or too high, you can change it by means of your MS Windows OS tools and in Denoiser Software directly. 1. Check the volume control level in your MS Windows OS. Set the playback level properly:

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Click Start button, Programs, Accessories, Multimedia and Volume Control. Make sure that Wave Output does NOT have Mute checked, that the volume is high enough and that the balance control is in the center. Check that Volume Control level (in the far left) is high enough and that the balance control is in the center. Also, make sure that the connection being used for input, usually Line-In or Microphone, is NOT selected to avoid playing the unprocessed and the processed audio simultaneously. 2. Check the current volume control level at the bottom of the working window of Denoiser

Software . The slider should be at the right side of the scale. Voice Output is Distorted 1. Check that the original sound in the source file has not too high level. To do it, listen to the

source file clicking a green button in <Control panel> tool bar. 2 If you use <Professional> mode, check that <Amplification> parameter is not too high. See Manual Adjustment of Noise Reduction.

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3.Check Sound Board Mixer options in your MS Windows OS. Click Start button, Programs, Accessories, Multimedia and Volume Control. Make sure that Wave Output does NOT have Mute checked, that the volume is high enough and that the balance control is in the center. Check that Volume Control level (far left) is high enough. Also, make sure that the connection being used for input, usually Line-In or Microphone, is NOT selected to avoid playing the unprocessed and the processed audio simultaneously.

4.Set Denoiser parameters to default values by clicking button. 5. If after all aforementioned operations the output sound has not good enough quality and you are sure that it is an effect of harmful noise, you can try to change standard noise cancelling filter parameters in order to get better results. See Editing of the Signal Processing Filter Parameters. Note: For some noisy speech files with high sampling rate (44100 Hz or higher) better filtering results may be provided by setting <Music> value in <Type of sound> option.

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User Support STC developers are always ready to assist you. In case of any questions, please don’t hesitate to contact us.

WWW: http://www.speechpro.com E-mail: info@speechpro.com Fax: +7 812 3279297 Phone: +7 812 3258848

We hope that you would like our product! Please note that we are always ready to develop any customized software for you. Any questions on our products and development costs should be addressed to our Sales department: e-mail: sales@speechpro.com).