A BRIEF OVERVIEW OF THE SCIENCES OF SOUND

Intro to SoundPart 2

1

Echo and Reverberation

Echo – a discrete reflection of a sound...it is intelligible

Reverberation – a “cloud” of reflections that are indistinguishable (Holman) A little bit of reverb creates a “bloom that subtly

reinforces words and notes” (Cox)...but too much reverb makes sounds unintelligible

“Echo and Reverb” video (1:16)

2

Inverse Square Law3

Source: http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.html

The Inverse Square Law4

The Inverse Square Law

Image from Howard & Angus (2009)

5

Boundaries

Image from Howard & Angus (2009)

6

Influences on Sound Propagation(see Holman Ch. 1)

Source radiation patternAbsorptionReflectionDiffractionRefractionConstructive and Destructive Interference

and BeatingDoppler Shift

7

Break

NOTE: Slides that follow are adapted from Rick Pitchford’s COM 353 slides.

8

Waveform Clipping:

Transfer Characteristics of all amplifiers are “S” shaped, curved and flattened at the ends, distorting the output signal if the input is too large. Amplifiers are meant to be used in their linear range to avoid distortion. (When you “go to 11” this may involve distortion!)

Maximum Positive Output

Maximum Negative Output

Gain Compression:

unity gain2:1 gain ratio4:1 gain ratio

knee

threshold

Automatic Gain Control allows the dynamic range of a signal to be reduced. This

can be used to maximize signal intensity while

preventing signal overloads. As the input

signal level passes a set threshold value, a knee is encountered in the transfer characteristic. Beyond the

knee, the gain of the amplifier is lower.

-- GOOD: Speaking BAD: Symphonic orchestra There is also gain expansion NOT the same as BRR compression!

Microphone Frequency Response: (X = frequency, Y = amplitude)

Shotgun, Dyn

Desk, Omni, Dyn

deci

Bel

s -

5dB

per

mar

k

Lav, Omni, Cond

Lav, Omni, Cond

Images from ElectroVoice Corp. documentation

deci

Bel

s -

5dB

per

mar

k

20 100 1K 10K 20K20 100 1K 10K 20K

11

Frequency Equalization:•Frequency equalization is achieved by passing a signal through an amplifier or passive component block with a variable frequency response:

•el-cheapo “tone” control:very limited high-frequency adjustment

•bass and treble controls:low and high frequency level adjustment

•graphic equalizers:placement of slider controls approximates the resultant frequency response

•parametric equalizers:sub-octave resolution and ability to fine-tune the amplitude of each individual frequency band

Frequency

Out

put L

evel

Frequency

Out

put L

evel

Out

put L

evel

Frequency

Frequency

Out

put l

evel

Input Signal

The Goal of EQ:

Change a signal with a sub-standard spectral balance or frequency response by sending it through an amplifier with a variable frequency response.

The output signal has a reshaped, hopefully improved, frequency response.

Frequency

Out

put L

evel

Result

Frequency

Out

put L

evel

EQ Block

•EQ can be used to “flatten” a signal with poor frequency response

•EQ can correct a signal with “path problems” (e.g., long lines = high freq roll-off; recorded on tape)

•EQ can be used for effect (AM radio sound, telephone, etc.) or sweetening (boosting low and/or high frequencies)

•In all cases, don’t over-do it; Less is More

EQ Examples:

sound files from http://www.dougyoungguitar.com/eq_pickuptest.htm

Flat, asrecorded

BassBoosted

MidBoosted

HighsBoosted

Telephone “Good”EQ

end15