19 Apr
2011
19 Apr
'11
1:05 a.m.
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(a)wolfdream.ca> wrote:
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
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.