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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
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Groove Geometry
Coarse groove with LP stylus
Stylus contacts debris field = Noise
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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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Vertical Tracking Force
Example of simple balance beam VTF gauge
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Vertical Tracking Force
Example of built-in VTF gauge
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Vertical Tracking Force
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
Trammel for Spindle-Pivot distance
Horizontal Tracking
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Horizontal Tracking
Angle
Trammel for Spindle-Pivot distance
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Vertical Tracking Angle
Vertical Tracking Angle (VTA) = red
Stylus Rake Angle (SRA) = green
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Vertical Tracking Angle
VTA adjustment affects
Stylus Rake Angle (SRA)
Tone-arm stability
VTA Adjustment is
Vertical
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Vertical Tracking Angle
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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Vertical Tracking Angle
Center of tone arm bearing ideally at height of record
surface
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Vertical Tracking Angle
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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Vertical Tracking Angle
Center line of SME tone-arm is actually drawn on arm
VTA level line
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Vertical Tracking Angle
Center line of SME tone-arm is actually drawn on arm
Check height
Front Back
Note: too high
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Vertical Tracking Angle
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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Vertical Tracking Angle
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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Tone-arm / Cartridge
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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Tone-arm / Cartridge
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
Tone-arm / Cartridge
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Tone-arm / Cartridge
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