Re: [ecasound] full-duplex sync

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Subject: Re: [ecasound] full-duplex sync
From: John Denker (
Date: Mon Oct 15 2001 - 18:45:49 EEST

At 04:57 PM 10/14/01 +0300, Kai Vehmanen wrote:

>In any case, without support from the hw-level, there's always a small
>error (in modern computers a _lot_ happens during 20usecs). But for
>practical (musical) purposes, delays below 1ms (1000usecs, ~44 samples)
>are not noticable.

1a) I understand that it is nice to support a wide range of hardware.
1b) I understand that some hardware doesn't support hardware sync.
1c) Therefore I agree that a non-hardware-based approximate-sync mechanism
is wonderful feature.
1d) If the foregoing is supposed to be a rationale for not supporting
hardware sync, I don't understand. The presence of one feature does not
prove that another feature is useless. Some hardware (including my
hardware :-) does support exact hardware sync.

2) The fact that computers are fast (a lot happens in 20 microseconds)
should make software-sync _more_ accurate, not less. So I don't understand
this part of the argument, either.

3) I'll not comment on the argument about "musical" purposes.

4) My team has a purpose, a very practical purpose, which requires highly
accurate sync. We are looking at echoes. Shifting the return signal by
one sample is noticeable, and shifting it by two or three samples (at
44100Hz) changes the result by 200%.

Recommendation: When designing sync schemes, please be aware that the
requirements are sometimes quite strict.

Sub-recommendation: If/when hardware sync is available, it may be the
easiest and best way to achieve excellent sync.


Today I will download the latest ecasound and see if the recent mt-sync
improvements meet our requirements.

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