Re: [LAU] New release of jack_delay

On Mon, Apr 18, 2011 at 05:21:46PM -0400, Paul Davis wrote:
> On Mon, Apr 18, 2011 at 4:52 PM, S. Massy <lists@email-addr-hidden> wrote:
> > Thanks,
> > Builds and runs fine on Debian Wheezy AMD64. What latency would be
> > considered average? What numbers should one expect?
>
> the "excess" value is generally on the order of several tens of
> samples in each direction. it can reach as high as the low hundreds.
> with USB audio (and potentially some firewire devices, the excess can
> even get up into the thousands, but its dependent on a variety of
> factors. this assumes you are doing the obvious thing and measuring a
> loopback via a D/A and A/D converter pair.
>
> for reference, my RME HDSP system, connected to a Frontier Designs
> Tango24 converter, meaures 68 samples of total excess latency, so
> about 34 in each direction.

That's a very typical value.

If you have an HDSP or any other card with ADAT (or MADI) interfaces
it can be interesting to measure the excess latency with a digital
loopback as well.

If this is much less than the value obtained when going through
the DA/AD converters, then the difference is an indication of the
type and lenght of the anti-aliasing filters used in the converters.

If these filters are linear-phase (i.e. a symmetric FIR), then
each of them will add a delay equal to half the length of the
filter, so the excess delay is a measure of the filter length.

Values I've seen so far appear to be much less than e.g. the filter
lengths used by libsrc or zita-resampler at high quality settings.

Ciao,

-- 
FA
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