Subject: Re: [linux-audio-dev] MTC, SMPTE, etc.
From: Iain Sandoe (iain_AT_sandoe.co.uk)
Date: Sun Jul 23 2000 - 20:54:22 EEST
>>I'm doubly confused... I was under the impression that SMPTE resolved to
>>"bits" which are 1/80th of a frame (at whatever frame rate we are using)...
>
> Ah. OK. I've used SMPTE-via-MTC so far, and I've never managed to find
> specs on the analog version of the signal. I assumed that SMPTE was
> limited to the same resolution as was represented in the MTC stream.
>
> Apologies if this is wrong.
I'm not an expert in SMPTE - this is just an observation based on the
systems that I have that accept SMPTE as a timing reference....
I used to use it a lot (before I had mutli-track digital recording) to sync
my old analogue 8-track to my midi stuff... this, at least preserved to
sound quality of the keyboards & synths..
>>i.e. approx. 0.5 ms
>
> but still pretty weak as a timebase for positioning an audio stream, eh ?
This is possibly getting a bit off-topic - but IIRC the ability to
synchronise to such an analogue stream is really only limited by the SNR in
the input stream (whether that is related to the source, recording medium
jitter or just loss of SNR in 'transmission'.)
If you have a copy of Gardener "Phase-locked Loop design" (I've 'lost' mine
:-( ) that would probably clarify all of this...
=====
Mind you, the bottom line is that I agree that SMPTE is not a helpful
synchronisation technique for audio... It is very useful to support it,
because it aids the inter-working of audio & video & it is an accepted and
widespread standard..
**but** it must be about the most "un-musical" time representation I have
ever come across - I'd much rather have linear hours:mins:secs than getting
confused below by frames & bits (where frames depends on the direction of
the wind :-)
Iain.
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