Re: splicing tape


Subject: Re: splicing tape
From: KEVIN AUSTIN (KAUSTIN@vax2.concordia.ca)
Date: Thu Feb 25 1999 - 05:57:17 EST


Larry asked (in part)

>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

I have read about this, and seen it tried, but at 38 cm/sec, a 1.9 cm
splice (3/4 inch) cross fades in 50ms! Tape to tapehead contact becomes
very iffy.

> 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?

My understanding (and experience) is that almost all tape splices
introduced distortion. Since it is almost impossible to get the bias
frequency bewteen the two pieces of tape in phase, there is a disruption.
(see also below). I have noted (apparently) that this disruption, in
conjunction with certain kinds of tape heads, causes a damped low
frequency oscillation of a few cycles at the edit.

In cleaning up an old (early 60s) tape piece, I went through checking
every splice, and used a high-pass filter (20 Hz cutoff), to eliminate
the 'thump'. It was displaced on the two channels, by the offset caused
by a 45 degree splice.

After 'cleaning up' the inaudible thumps, the piece had a much 'cleaner'
sound.

>2. Assuming that only amplitude is affected by such a diagonal
>splice and that it is a full-track, fully saturated/recorded tape, can
>I deduce that a kind of zig-zag splice would still only affect
>the amplitude and that such multiple ramp splice patterns
>would simply cause the amplitude ramps to be summed and
>not create some special distortion in the material?

Hugh Le Caine once discussed some of the difficulties related to this in
terms of the mechanics of the tape<->head contact. Since the splice
creates a region of greater friction, there is 'jitter' introduced, which
translates as fm (stick and slip). Also, the cut deforms the surface of
the tape, and lifts it (ever so slightly) off the heads, introducing am.

[The longer the cut, the greater the effect. Towards the end of analog
recorder days, the prefered edit angle changed from 45 to 60 degrees (or
perhaps even 75?)]

These mechanical artifacts may be part of the 'beauty' of tape pieces,
adding to their lyric, poetic nature.... >8-[] ?

You may want to look at some of the edits in a digital editor.

Best

Kevin
kaustin@vax2.concordia.ca



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