Re: splicing tape


Subject: Re: splicing tape
From: Eric Somers (somers@sunydutchess.edu)
Date: Wed Feb 24 1999 - 10:55:55 EST


Dear Larry,

At 05:37 AM 2/24/99 -0600, you wrote:
>1. With sound material recorded on quarter-inch tape
>on a "full-track", mono tape machine, it is my understanding
>and recollection in practice and playback that a long diagonal
>splice between source material A and B would cause material
>A to decrease to zero amplitude as material B ncreased to
>full amplitude: a simple cross-fade Question: does the long diagonal
>splice
>have any other effect than amplitude change on A and B; e.g.,
>distortion of the signal or loss/gain of sideband components?

The condition you describe is a form of fast crossfade. Of course, in any
situation where two signals are being mixed there will be timbre changes to
the first source when the second source is brought in due to phase
cancellation/reinforcement of common frequencies, the way the ears perceive
the additional harmonic content, etc. This would, of course, result in
some distortion, or change, of the original signal during the crossfade
period. In most diagonal splices this crossfade is extremely fast since
most of us who composed with analog tape used at least 15 ips (sometimes 30
ips before noise reduction was invented).

Here is a thought experiment. Suppose signal A consists of a single 200 Hz
sine wave. Signal B consists of a 200 Hz sine wave 90 degrees out of phase
with Signal A. As more and more of Signal B is brought it, during the
period in which both signals are easily audible, there will be considerable
interaction of the two slightly-out-of-phase 200 Hz signals producing a
more complex wave. Yet before and after the crossfade the signal will be
nothing more than a "pure" sine tone.

Although a zig-zap slice would produce a much different end result, in the
proposed experiment above, than a simple diagonal one, it would have to be
awfully long (as physical splices go) to be perceived by most people's
ears. This would be an interesting experiment, however, (I might try it
myself) and easy to simulate in a hard disk sound editing program, like
Sound Forge, that allows one to create unusual crossfades.

A very intriguing question.

- Eric



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