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Proper Playback of 78 rpm Records

There are three factors which must be taken into consideration when playing 78s:

  1. groove widths have varied over the years
  2. playback equalizations varied until they were standardized in the mid 1950's
  3. recordings were not made at a speed of exactly 78 rpm until the mid 1930.

Proper stylus size

There was a gradual decrease in the groove widths of 78s throughout their production history owing to gradual refinements in the recording process. Proper contact between stylus and groove walls is essential to obtain optimum sound quality during reproduction. Thus it is important that the proper size and shape of stylus be chosen for optimum-quality playback.

Also, by choosing the appropriate stylus, one can compensate for different types of wear. For example, a smaller stylus can be used to track lower into the groove to compensate for a record with upper groove damage. In some instances tracking different parts of the groove will not make much difference, but in other instances there will be a remarkable improvement.

Some experimentation with different styli, listening for clarity of sound and amount of background noise, will illustrate the importance of choice of stylus. The National Library of Canada has about 24 styli, but 3 or 4 should be adequate for most uses.

Proper playback equalization

Every modern (post-1955) power amplifier has two components built into the phono input: a preamplifier to boost the low level signal from the cartridge, and a built-in equalizer set to the Record Industry Association of America (R1AA) standardized playback equalization curve. It is the latter of these that can present some problems to 78 playback.

This equalizer cuts high frequencies and boosts bass frequencies; the standard determines at which frequency this begins to occur.

At the high end, the process functions to counteract the fact that high frequencies are boosted (i.e., exaggerated) during mastering to act as a form of noise reduction during playback. When a disc is played back through an RIAA standard phono preamplifier, the high frequencies are cut by the same amount they were boosted in the mastering process restoring the high frequencies to their proper levels and, consequently, proportionally cutting high frequency surface noise.

Likewise, at the low end, low frequencies are reduced during mastering to reduce groove modulation distance. (Low frequencies require more power to propagate which requires larger groove modulations.) This allows a more dense winding of grooves, thus allowing for longer playing time and prevents grooves from running into each other. At playback, through the equalization, the low frequencies are boosted by the same amount which they were reduced during the mastering process, restoring the low frequencies to their proper levels.

This built-in equalization, with its set playback filtering curves, must be by-passed to properly play 78s. 78 rpm record playback equalization ranges from none (acoustic: no cutting or boosting of frequencies) to RIAA equalization. Playback curves varied from company to company and varied within companies.

To playback a 78 with proper equalization, an Owl 1 Restoration Module can be used. The Owl 1 has a phono preamplifier so that the output of the cartridge can be plugged directly into the Owl. The Owl output is then plugged into an auxiliary input of the amplifier, effectively by-passing the power amplifierís phono input. The Owl consists of a low frequency "Turnover" knob which boosts bass frequencies below a certain level and a high frequency "Rolloff" knob which attenuates high frequencies above a certain level. Also included is an RIAA setting. The Owl comes with guidelines giving proper playback equalization for various record labels throughout time.

Proper playback speed

Though referred to as 78s, the 78-rpm speed did not become standard until the mid-1930ís. Variations in speed will change the recordings pitch and will make a remarkable difference to the timbre of a recording. A 5% difference is equal to approximately a semitone (the note A becomes an A flat and so on). A "78" recorded at 76.6 rpm must be played at 76.6 rpm for proper reproduction.

Determining proper playback speed can be difficult. Having a score to determine the correct key is a good start. Unfortunately singers had no qualms about transposing a piece to fit their voices, and, of course, not all recorded music is available on sheet music. Also, "concert A" pitch, now A=440Hz, has varied over the years (and is in the process of changing now throughout the world). Keep in mind, when pitching 78s, that stringed instruments prefer sharp keys and brass instruments prefer flat keys. When pitching a vocal recording listen carefully to the singerís diction, resonance and vibrato speed.

Noise Reduction

Using the proper stylus and equalization and accurate pitch will result in a good quality 78 rpm reproduction. However, if more complex filtering is required, a Packburn Audio Noise Suppressor can be used to remove transient noises (i.e., pops and clicks). Though expensive,it is a useful device. As the Packburn works best when the signal arrives directly from the cartridge amplified but unfiltered (flat), a phono preamplifier made by Stanton (Model 310) can be used. Once filtered by the Packburn the signal can then be routed to the auxiliary input of the Owl 1 for proper equalization.

Finally, if you really want to do a "bang-up" job and happen to have a spare $120,000, you would wish to consider purchasing a CEDAR (Computer Enhanced Digital Audio Restoration) system. This computer system, developed in Cambridge, England, removes pops, crackles, hiss etc., miraculously well. You'll be the envy of the neighbourhood!

Gilles is Audio Conservator, Music Division, National Library of Canada, Ottawa, Ontario, and a member of CAPS.