Record pressing materials. Certain record pressing materials - notably that of brown Perfects (14200 - 14900) resent insertion of pins, but the addition of post-1932 EMI pressing material will ameliorate.

2. PITCH CORRECTION

Not all "78"s are actually recorded at 78 revolutions per minute. While Edison's "diamond discs" are remarkably consistent at 80 r.p.m., other companies have been less consistent - usually by reason of unreliable power source or of ill-controlled elements such as lubrication or even weather! In early days, differences in recording speeds could be attributed to compromise between duration of performance and space available - (Pathe).

Variation in recording speeds were largely ignored in the days of "78" dubbed reissues when the pitch of the dubbing was directly related to that of the original. However, it has long been apparent that reproduction at correct pitch is essential to correct perception of the performance.

Although, in the past, musical pitches have varied (Steinway specified C517 c/s, "Old" Philharmonic pitch called for A452 and a half c/s) but, although some English Brass Bands continued to use the Old Philharmonic pitch through the first half of the last century, generally the New Philharmonic pitch at C522 to C523 or A440 has been that accepted as the norm since before the advent of sound recording and reproduction.

The most reliable clue to pitch is found in the vowel sounds of the human voice which remain a useful constant regardless of language. Even so, it is often difficult to discern exactitude within a semi-tone, and other yardsticks will be necessary to assist a closer approach.

While the classic music fraternity may feel unhappy when trying to relate the pitches employed by earlier composers to a modern equivalent, the performances during the sound recording period present less of a problem.

There is a period in "popular" music during which band leadership tended to dictate a change in keys employed. During the first quarter of the last century, leadership was dominated by the violin and consequent use of "sharp" keys whereas, with the ascendancy of leadership by brass or reed instruments after 1920, keys employed became predominantly "flat".

Comparison of apparent keys employed throughout a recording session during which recording speed seldom varied significantly will usually serve to show up unlikely keys and suggest an adjacent set. If doubt persists, this may be settled by making a judgement upon the feasibility of a given phrase being mechanically possible for the instrument concerned or, in the case of a reed instrument, the transition from one register to another.

For the most part, therefore, in recordings of musical instruments and a voice, three areas of consideration will almost certainly establish the pitch of the performance. There will, of course, be recordings involving, for instance, voice and guitar only when no reference has been made to any standard pitch as the instrument was tuned: others involving voice and piano when the pianist may or may not have the ability to accompany in unexpected keys. A solo voice recording may have no relationship to any standard pitch and may even vary during the performance in which case reference to another recording of the same voice in known pitch may be the only clue to be followed.