On 14.03.23 07:16, Worik wrote:
During the pandemic I tested a lot of USB sound cards on Linux -
actually the Focusrite Scarlett Solo was one of the best in terms of
latency (and also in terms of interrupt timing jitter - this is crucial
when it comes to very low latency and high CPU load):
https://github.com/gisogrimm/ovbox/wiki/Soundcards
That is really interesting.
Two questions come to mind:
1) How did you measure that?
https://github.com/gisogrimm/ov-client/blob/master/tools/gethwdelay.sh
It is basically a wrapper around jack_delay (which, as far as I know,
was written by Fons).
2) How do I interpret it? Naively it seems Focusrite Scarlett Solo is best at 2ms. What are the other two columns?
The idea behind this table is to know what delay is added to the
theoretical minimum delay for block-wise audio processing. This differs
significantly between audio devices.
It measures the round trip delay, i.e., the delay one would get from a
microphone to the headphones if no delay is introduced by the signal
processing (e.g., reverb, filters). The second column is the period size
configured in jack ("P" in the email from Fons), and the next two
columns are the delays, first in audio samples, and then converted to
milliseconds (this is just the first number divided by 48).
Depending on your system you will get tons of underruns when using the
smallest period sizes. On a Raspberry Pi 4 the Scarlett Solo runs well
with P=48 at 48 kHz sampling rate and a jack load of about 30-40% (jackd2).
With the HiFiBerry GPIO caps I get an even better performance, both in
terms of latency and jitter.
I have been tempted by the HiFiBerry, I am put off as it seems "line in" is not front of mind for them. It is for me. How have you found it? Is the sound quality OK?
The same Raspberry Pi 4 runs stable at 192 kHz and P=48 with 18% jack
load using a HiFiBerry GPIO sound card, which results in the shortest
delay I could achieve with jack on a Raspberry Pi 4.
I use the HiFiBerry only for DA, not for AD (although the offer ADCs as
well, AFAIK). The sound quality is good, the cheapest ones have only
asymmetric outputs which may result in a bit of humming noise. The XLR
output version has very low noise, but I did not measure it (nor any
other properties).
Best,
Giso
Best,
Giso
Pi Sound and Modep: https://blokas.io/ https://blokas.io/modep/
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