Re: splicing tape


Subject: Re: splicing tape
From: Lawrence Casserley (leo@chiltern.demon.co.uk)
Date: Thu Feb 25 1999 - 06:10:06 EST


In message <199902241600.LAA05010@clyde.concordia.ca>, Eric Somers
<somers@sunydutchess.edu> writes
>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).

But this is true of any cross fade. There is no inherent distortion
caused by the tape splice method. We had full track mono machines at the
Royal College of Music in the late 60s and used this technique a bit. To
be more precise, the magnetic analogue of the waveform is recorded
across the whole tape, so what is happening is that the width of one
recording is decreasing as the other increases. Therefore the amount of
magnetic disturbance changes. The waveform, which proceeds along the
tape, is not changed. The problem is that you need very long splices to
do anything more than soften the transition. Even a quarter second at 15
ips lasts 3.75 inches - very hard to cut accurately. Longer crossfades
were usually done manually on the mixer. Precise alignment of tapes (and
the coordination of assistant button pushers) became a major studio
skill when creating complex montages.

Lawrence Casserley

-- 
Lawrence Electronic Operations -Tel +44 1494 481381 -FAX +44 1494 481454
Signal Processing for Contemporary Music -email leo@chiltern.demon.co.uk
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