AES 78-rpm calibration disc set

[last updated 2007-08-09]

Calibration Disc Set for 78 rpm Coarse-Groove Reproducers - Content

Click here for a more detailed discussion of the purpose for the the discs. To purchase this Calibration Disc Set, please go to the Special Publications area in the AES Web store.

AES Cat. No. AES-S001-064
Boxed set of 2 identical 12-inch vinyl discs (working copy and reference copy)

SIDE A: Gliding tone, 20 Hz to 20 kHz

Speed: 77,92 rpm
Lateral (mono) coarse groove
Time constants; 3180/450/0 ms
Separate outer and inner bands, each comprising:

1 kHz trigger tone;
Gliding tone, 20 Hz to 20 kHz;
1 kHz reference level*

*20 mm Light Band Width (LBW); approx 8 cm/s peak, 5,7 cm/s rms

The gliding tone, or sweep, is timed at 50 s to allow synchronisation with Bruel and Kjaer (B&K) equipment, such as response Test Unit 4416 and Recorder 2305/7, and other equipment with a similar facility. An initial 1 kHz tone before the sweep provides the automatic start signal for the B&K system.

The nominal level for the gliding tone is 10 dB below the 20mm LBW tone.

The level tolerance on the sweep is approximately +/- 1 dB. The main purpose of the sweep is to reveal any sudden departure from an even response such as might be caused by resonances within the playback system.

The sweep and reference tone is repeated at a smaller diameter to allow measurement of playback tracing losses.

SIDE B: Single tones, 18 kHz to 30 Hz

Speed: 77,92 rpm
Lateral (mono) coarse groove
Time constants: 3180/450/50 ms

Fixed tones 18 kHz to 30 Hz. Level at 1 kHz (0 dB in the recorded characteristic curve) is +5 dB above 1 cm/s rms stylus velocity.

The curve employed (see chart below) is the "Coarse Groove" curve specified in IEC Publication 98 Ed.2; also British Standard 1928:1955. Time Constants: 3180/450/50 msec. For frequencies above 10 kHz, levels are reduced by 6 dB. All frequencies are announced.

     1 kHz   0 dB
    18 kHz  +9,25 dB
    16 kHz  +8,25 dB
    14 kHz  +7,25 dB
    12 kHz  +6,0  dB
    10 kHz +10,5  dB
     8 kHz  +8,75 dB
     6 kHz  +6,75 dB
     5 kHz  +5,5  dB
     4 kHz  +4,25 dB
     3 kHz  +2,75 dB
     2 kHz  +1,5  dB
     1 kHz   0 dB
    700 Hz  -0,75 dB
    400 Hz  -2,25 dB
    200 Hz  -5,75 dB
    110 Hz  -9,75 dB
     60 Hz -13,25 dB
     30 Hz -15,5 dB

From the original metal master, matrix No. CTPX 17791, that was made at Abbey Road Studios and released as catalogue number JGS 81 in 1955. Pressed under license from EMI Records Ltd.

A note on speed standards

For records with a nominal speed of rotation of 78 rpm, the International Standard IEC 98 of 1958 set a blanket tolerance of +/- 0,7 %. In fact, practical speeds were determined by the synchronous motors used for professional cutting equipment - such as the lathes made by Neumann, Scully, Presto, Lyrec, and Westrex. Because they were locked to the power supply frequency they provided a very precise rpm. Some equipment used slow-moving direct drive multi-pole motors to achieve the final speed, or they used mechanical gearing. In either case, the speed ratios could only be simple ratios of the power-line frequency, and were not identical when 60 Hz operation is compared to 50 Hz operation.

Recognising this, Edition 2 of IEC 98, published in 1964, stated speed tolerance more accurately:

Rated speed of rotation50 Hz electric supplies60 Hz electric supplies
Nominal 78 rpm77,92 rpm +/- 0,5 %78,26 rpm +/- 0,5 %
Nominal 45 rpm45,11 rpm +/- 0,5 %45,00 rpm +/- 0,5 %
Nominal 33 1/3 rpm33 1/3rpm +/- 0,5 %33 1/3 rpm +/- 0,5 %

Both sides of this record were cut on a lathe operating on 50 Hz power and so are clearly labelled, "77,92 rpm".

The speed error when replayed on a power-line-locked 60 Hz turntable would also be about +0,5 %, however such turntables are rare. even so, in its primary application of confirming the replay characteristic of a reproduction chain, the error contributed by a 0,5 % increase in reproduced frequency would be small. In practice, most turntables use friction drive idlers or belts - where the speed tolerance is more poorly defined - or employ a crystal-referenced direct drive that is independent of power-line frequency so that the speed may be adjusted to arbitrary precision and to compensate for any error.

IMPORTANT: vinyl pressing: Not for use with mechanical reproducers or earlier electrical pickups using steel styli. Use lightweight pickup only.

The pressings were made by Record Industry of Holland

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