Re: [linux-audio-dev] Total latency measurement tool

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Subject: Re: [linux-audio-dev] Total latency measurement tool
From: David Olofson (audiality_AT_swipnet.se)
Date: ke marras 10 1999 - 19:07:48 EST


On Wed, 10 Nov 1999, Paul Barton-Davis wrote:
> david - can you explain why the input/output level should have such a
> pronounced effect on the test ? i understand the idea of a threshold
> for detection, but it seems that moving the input gain or pcm volume
> up and down can have quite a substantial impact on the numbers being
> displayed. this seems counter-intuitive to me. it could be a side
> effect of my current super-crappy-video card too.

It shouldn't have much effect at all. If the SNR gets too low, or the
signal clips, it will affect the result, but other than that, it's
not very sensitive. There's a peak level meter that scales the trig
level automatically.

> for my trident 4d-nx card, i can get stable readings of about 32
> samples (using ALSA-OSS-emulation) - makes sense given the PCI burst
> size, doesn't it ?

32 samples total...? What fragment size and # of fragments?

> for my tropez+ (ISA bus), the test doesn't seem to work: it complains
> about the level being too low, despite everything being turned all the
> way up.

Strange... Do you get any output, and does the program react if you
feed something else to the input? (It should trig on any transients,
and even twice every period of low frequency signals.)

> these numbers involve routing the signal through a samson 24 track
> analog mixer, but i can't imagine that this should affect them given
> the measurement being performed.

Well, if there's any measurable latency at all, it should at least be
*very* constant...

//David

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