Equalisation table for 78s

Electrical recording replaced the acoustic method in 1925. Gramophone record sleeves informed the public of the benefits with theoretical claims such as the one above although in  practice it took another 20 years before such a wide range of frequencies could be reproduced in the home.

The specifications of the replay characteristics of several types of record are listed in this table. The recording characteristics are the inverse of the replay curves. If preferred, the table can be used to define pre-set characteristics for a graphic equaliser. In many cases the suggested setting should be used as a preliminary guide rather than a definitive recommendation. For labels not listed, try Westrex initially if record was produced after 1925.

Equalisation table for 78 rpm records

Specialised pre-amplifiers may be purchased at a high price from one or two suppliers who can be found from an Internet search. Equalised reproduction may also be achieved using a graphic equaliser configured to approximately the required settings. Tone control circuits consisting of bass and treble are rarely adequate. A simple pre-amplifier circuit that can be made by a home electronic constructor at reasonable cost is given elsewhere on this site.

Westrex was the original electrical recording system, licensed to various companies at a fee of around 1d (one old penny) per record. Records were made with a moving-iron cutter. Alan Blumein of Columbia introduced a moving coil cutter early in 1932. Its response was wider than the Westrex system and it enabled good recording of transients. Like all recording systems the final curve was resulted from a complex combination of electronic equalisation, electro-mechanical resonances and damping. Thus many of the the equalisation curves may not be as precise as they seem from the table above. Blumlein was also the inventor of "binaural" or stereo recording at about the same time.

Sources of information about the actual curves adopted by various recording companies are elusive. They all seem to be derived from similar unauthenticated sources - probably as is some of the data in the table above! Also, some of the stated stated characteristics are not realisable by simple C-R feedback at a gradient of ±6dB per octave. It may be preferable to use one of these curves for recording and then to tweak the result using a graphic or parametric equalisation software transform.

Here are some genuine e.q. curves. Victor was a US label which evolved its equalisation, Decca ffrr for post-War 78s is shown in the table above and the EMI "coarse groove" or 78 rpm curve was published on 1957. NAB was used for US Brunswick and is the nearest realisation of the ideal constant velocity recording curve, which would be a straight line of graident 6db/.octave.