Playback of Grooved Media

8/12/2019 Playback of Grooved Media

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2004-2008 Audio Ar chive, I nc.


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ARSC Annual ConferencePalo Alto, CA

Playback of Grooved Media :

Transfer MethodologyMarch 29, 2008

Eric Jacobs, The Audio Archive, Inc.


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Goals

Create awareness of

Disc cleaning and handling

Groove and stylus geometry

Disc playback parameters

Playback problems with damaged media

Set-up and alignment for modern and historical media

Terminology

Why important But not how to do it

Equalization and how it influences transfer decisions


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Cleaning and Handling

Significant cleaning solution research

Balance between chemical and mechanical cleaning

Disc Doctor solution as base for small batches

Tergitol solution as base for large batches

Use pharmaceutical grade distilled de-ionized water

Lacquersonly: Clear ammonia additive (2%)

Use a suction-type record cleaning machine like Monks

Keith Monks users need to protect suction wand bearing

Dedicated brushes for wash and rinse

Fully support disc during cleaning

Lacquers only: ALWAYS wear gloves

Lacquers only: minimize water contact time with disc

Lacquers only: clean both sides even blank sides


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Cleaning and Handling Record cleaning station


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Groove Geometry

Stylus and groove geometry

Example: 78 RPM Groove and Stylus


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Groove Geometry

Coarse groove with 78 stylus

Stylus contacts walls = Less noise



Groove Geometry

Coarse groove with LP stylus

Stylus contacts debris field = Noise



Groove Inspection

Coarse groove 78 played with LP stylus

LP stylus scratch

Inner Left Wall Outer Right Wall

Spindle / Label

Inner GroovesOuter Grooves


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Groove Geometry

Groove cutter geometry


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Groove Geometry

Tracing Distortion

Vertical distortionsecond harmonic, increases with frequency


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Groove Geometry

Pinch Effect

Lateral dimension changeVertical distortion, second harmonic


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Groove Geometry

Groove and stylus geometry

Cutter

Spherical

Elliptical

Line

Tracing and pinch distortion

Less tracing and pinch distortion

Least tracing and pinch distortion


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Groove Geometry

Vertical tracking distortion

Expanded fall, compressed rise

Compensated by standardizing on 15-degree cutter angle


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Groove Geometry

LP era15-degree SRA (Stylus Rake Angle)


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Groove Geometry

Coarse groove 78 era0-degree SRA


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Stylus Rake Angle

VTF = 4 gram + angle block (SRA = 0 deg)

15-degree

Angle

Block


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Groove Measurement

Predicting stylus geometry and size


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Groove Inspection

Cross-talk in an Edison Voicewriter disc


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Groove Inspection

Damage from stylus drop


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Groove Inspection

Damage from stylus drop


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Speed Types

Two types Constant Angular Velocity (CAV)

RPM is the same for all grooves

Constant Linear Velocity (CLV) Groove velocity at the stylus is constant

RPM slower at outer grooves, faster at inner grooves

CAV used for most discs Audio quality best at outer grooves

Example: LP, Shellac, Lacquer, Edison Voicewriter Note: Sequential lacquers often run inner-to-outer, then

outer-to-inner for smooth transition

CLV used to maximize recorded disc time Uniform audio quality from outer to inner groove

Example: Gray Audograph (dictation)


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Measuring Speed

Digital read-out

Strobe

Tachometer Calibration tone


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Measuring Speed

Direct read-out

Easiest

More expensive


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Measuring Speed

Strobe

Lower resolution

Low-Cost Simple but takes awhile to detect small speed

errors


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Measuring Speed

Strobe examples


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Measuring Speed

Strobe examples


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Measuring Speed

Strobe examples (my favorite by KAB)


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Measuring Speed

Non-contact tachometer

Precise (0.001 RPM resolution)

More costly Quick and easy to use


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Measuring Speed

Non-contact tachometer uses reflective strip


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Measuring Speed

Non-contact tachometer in use


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Measuring Speed

Calibration Disc Not as accurate for speed

Requires more specialized equipment Multi-meter with frequency measurement

Cables to connect multi-meter to phono preampoutput

Can digitize and keep as record of

Rosetta Tone or system signature Frequency response

Noise and distortion

Cartridge loading / damping


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Speed Change in DAW

Pitch change in semitones

V1 = current speed (RPM, Hz)

V2 = desired speed (RPM, Hz)

Semitones = 1200*LOG(V2/V1)/LOG(2)

Example: playback a 78.26 RPM shellac at 33.33RPM, digitize, and then re-pitch in the DAW with a14.78 semitone pitch change

Note: do not use preserve length option in Wavelab


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Fine-tuning Speed

Low torque motor tips

Sensitive to temperature

Motor heats up over time, winding resistance increases,

torque is reduced, turntable slows down0.1 to 0.2 RPM

effect

Shows up as speed drift over time

Sensitive to stylus friction

Coarse groove discs offer substantial friction resistance0.1 to 0.2 RPM effect

More friction at outer grooves (function of linear speed)


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Fine-tuning Speed

Can you hear a speed change?

Generally, the human ear can detect an 8 cent

pitch difference

33.33 vs 33.43 = 5 cent

33.33 vs 33.53 = 10 cent

78.26 vs 78.36 = 2 cent

78.26 vs 78.46 = 4 cent


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Alignments and

Adjustments

VTFVertical Tracking Force

Affects sound quality, anti-skate, and SRA

AntiskateLateral Tracking Force

Compensates for inward lateral force

HTAHorizontal Tracking Angle

Controls distortion profile

VTAVertical Tracking Angle

Affects SRA and tracking stability

SRAStylus Rake Angle

Vertical offset angle of stylus with disc surface

Azimuth

Affects channel separation / cross-talk most


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Vertical Tracking Force

Affects sound

Alignment of coils and magnets

Affects tracking performance

Suspension travel

Skating forces Stylus rake angle (SRA)


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Example of simple balance beam VTF gauge


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Example of built-in VTF gauge


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Example of digital VTF gauge (0.01 gram

precision)

Stylus rests on

light gray disc


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Anti-skate

Lateral skating force is a vector component

of stylus friction

Skating Force

Stylus Friction

PlatterTone-arm

Anti-Skating Force


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Anti-skate

Increasing groove amplitudeincreases

Stylus Friction

Increasing

Skating Force

Increasing Stylus

Friction

PlatterTone-arm

Anti-Skating Force


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Anti-skate

Increasing groove speedincreases Stylus

Friction

Increasing

Skating Force

Increasing Stylus

Friction

PlatterTone-arm

Anti-Skating Force


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Anti-skate

Example of spring anti-skate


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Anti-skate

Example of weight anti-skate

H i t l T ki


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Horizontal Tracking

Angle

Deviation of cantilever from groove tangency (when

looking from above the cartridge)

Deviation resultsin geometric tracking distortion

H i t l T ki


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Horizontal Tracking

Angle Pivoted tone-arm

Discs grooves are cut on a linear tracking lathe

Pivoted tone-arm introduces tracking distortion

Cost-effective to manufacture

Easy to operate

Tracking distortion can be minimized but not eliminated

H i t l T ki


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Horizontal Tracking

Angle Linear tracking tone-arm

No tracking distortion (offset angle = 0)

Highly sensitive to level and linear track friction

Expensive to manufacture and operate

H i t l T ki


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Horizontal Tracking

Angle

Choice of HTA determines locations of nulls Null points are points of zero tracking error

Loefgren Distortion Curve Minimize distortion between nulls

Higher distortion at inner and outer grooves

Baerwald Distortion Curve Balance max distortion between nulls and inner/outer

grooves

Stevenson Distortion Curve Modified Baerwald

Places inner null at inner groove

H i t l T ki


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Horizontal Tracking

Angle Baerwald versus Loefgren alignment (LP)

Loefgren

(a) Less distance between nulls

(b) Max distortion between nullsis lower than Baerwald

(c) Max distortion at inner/outer

grooves is greater than

Baerwald

Baerwald

(a) More distance between nulls

(b) Max distortion is same

between nulls and at

outer/inner grooves

Red = RMS Tracking Distortion (%)

Blue = Tracking Error (degree)

Null Point = Zero Tracking Error

H i t l T ki


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Horizontal Tracking

Angle

Stylus

Cantilever

Tone-arm

Effective

Length (Le)

Pivot

Spindle

Stylus

Mounting

Distance

(Lm)

H i t l T ki


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Horizontal Tracking

Angle

Terminology

Le Effective Length (Pivot-Stylus)

Lm Mounting Distance (Pivot-Spindle)

Theta Offset Angle (cantilever angle)

D Overhang (Le Lm)

N1 inner null radius

N2 outer null radius


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Horizontal Tracking


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Horizontal Tracking

Angle

Sensitivity Analysis

Error Distortion Increase Pivot-Stylus (see overhang)

Pivot-Spindle (see overhang)

Offset Angle 3 deg 2.00%

Overhang 1 mm 0.12%

Conclusionfocus alignment efforts on offset angle forgreatest impact


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Horizontal Tracking


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Horizontal Tracking

Angle

Trammel for Spindle-Pivot distance

Horizontal Tracking


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Horizontal Tracking

Angle


Horizontal Tracking


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Horizontal Tracking

Angle



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Vertical Tracking Angle

Vertical Tracking Angle (VTA) = red

Stylus Rake Angle (SRA) = green


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VTA adjustment affects

Stylus Rake Angle (SRA)

Tone-arm stability

VTA Adjustment is

Vertical


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Influence of VTA on SRA

5 mm change in pivot height = 1 deg change in SRA

Note: 1 gram change in VTF = 3 deg change in SRA

(depends on compliance of cartridge)

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

VTA offset (mm)

SRA

offset(deg)

9-inch arm

12-inch arm


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Stylus Rake Angle

VTF = 3 gram (SRA = 13.8 deg)


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Stylus Rake Angle

VTF = 4 gram (SRA = 16.6 deg)


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Center of tone arm bearing ideally at height of record

surface


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Tone-arm STABLEif bearing center is BELOWrecord surface

Tone-arm LESS STABLEif bearing center is ABOVErecord

surface

VTF

Stylus Friction

VTF

Stylus Friction


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Center line of SME tone-arm is actually drawn on arm

VTA level line


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Center line of SME tone-arm is actually drawn on arm

Check height

Front Back

Note: too high


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Variability in cartridge dimensions

Stylus-to-cartridge-mounting-bolt distance

varies from 8.5 to 10 mm

Stylus-to-top-

of-cartridge


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Variability in cartridge dimensions

Ortofon SPU-GT with mounting block (4.0 gram VTF)

21.60 mm

Lyra Helikon SL(1.8 gram VTF)

17.85 mm

Shure M44-7(2.0 gram VTF)

17.90 mm

Shure V15 Type VXMR(1.0 gram VTF)

17.10 mm


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Azimuth

Primarily affects channel separation / cross-talk

No real affect on channel balance

Using a test disc LEFT channel signalmeasure LEFT output (V1-L)

RIGHT channel signalmeasure LEFT output (V2-L)

LEFT channel signalmeasure RIGHT output (V1-R)

RIGHT channel signalmeasure RIGHT output (V2-R)

Cross-talk-L = 20*log(V1-L/V2-L)

Cross-talk-R = 20*log(V1-R/V2-R)

Minimize either Cross-talk-L or Cross-talk-R

Tone-arm / Cartridge


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Resonance

Resonance impacts susceptibility to tracking problemsfrom external vibration and music to cueing

Typical resonance is 5-12 Hz

Building vibration, warp and footfall is 2-6 Hz

Lowest musical frequency is 16 Hz

Tonearm and cartridge form a mass-spring system

Effective tonearm and cartridge mass at the stylus

Cartridge suspension acts as a spring

Rules of Thumb Keep resonance between 6 and 16 Hz

Resonance >= 16 Hz (sensitive to distortion)

Resonance


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Resonance

Calculating resonance frequency

RF = 159 / sqrt ( (eff. mass + cart mass + fastener mass) *(compliance) )

RF (Hz): resonant frequency

eff. mass (gm): rated by tonearm manufacturer

cart mass (gm): rated by cartridge manufacturer, or you can

measure this with a scale fastener mass (gm): screws, nuts, spacers, washers, shims.

Compliance (x10E-6 cm/dyne): stiffness value rated by cartridgemanufacturer



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Resonance

Measuring resonance frequency

HFNRR (Hi-Fi News and Record Review) Test Record

provides good tools


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Vibration Isolation

Prevent external noise

Improve cartridge tracking 5-12 Hz tonearm-cartridge resonance

2-6 Hz building vibration and foot fall

Most consumer isolators are insufficient Most turntable suspensions are insufficient


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Vibration Isolation

Minus K Atomic Force Microscope (AFM) isolator


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Vibration Isolation

Minus K Atomic Force Microscope (AFM) isolator


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Equalization

Increase playing time

Increase frequency response Reduce high frequency noise


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Equalization

Bass EQ - Record

Attenuate low frequency groove amplitude Grooves can be closer together = longer playing time

Bass EQPlay

Increase low frequency groove amplitude Low frequency signal is at correct original level

Stylus can better track low frequency grooves


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Equalization

Treble EQ - Record

Increase high frequency groove amplitude High frequency signal is above high frequency noise

Treble EQ - Play

Attenuate high frequency groove amplitude High frequency signal is at correct original level

High frequency noise is attenuated


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Th k


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Thank you

Eric Jacobs

The Audio Archive, Inc.Tel: (408) 221-2128

[email protected]

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Playback of Grooved Media