28 Sep
2018
28 Sep
'18
1:51 p.m.
On Mon, 24 Sep 2018, Holger Marzen wrote:
On Mon, 24 Sep 2018, David Kastrup wrote:
Or you can simply wait til the "right" moment und use the original
values. But that would not use more CPU depending on the quality
setting. So there seems to bee an interpolation happening.
It looks as if I have to do a looptest (play through the 2nd interface
and record with the 1st) to get an impression how's the signal distorted
at the different quality settings.
I used the interface that's connected via audioadapter for playback and
the "main" interface that's directly controlled by jackd for recording.
As a signal source I used Audacity with generated sine waves of 5000 and
10000 Hz. I played this signal and recorded it (audio cable between
interfaces). The result showed that the signal gets indeed resampled and
that the quality setting matters.
q0 (SRC_LINEAR) and q1 (SRC_ZERO_ORDER_HOLD) showed a non-flat envelope
of the recorded signal - bad.
q2 (SRC_SINC_FASTEST) showed the desired flat envelope and seems to be
the best compromise between CPU load and quality.
-> That's the setting I'll use from now on.
I cannot to further examination because the spectrum analyzer in
Audacity can't show the harmonics accurately. I expect a single peak in
a sine wave's spectrum but I got a softer curve.
SRC seems to bee an abbreviation for Secret Rabbit Code
http://www.mega-nerd.com/SRC/
Holger Marzen <holger(a)marzen.de> writes:
The output of the first adapter is used for
- direct monitoring
- headphone monitoring and mixing/mastering, but without EQ
As I
played around with the quality setting (-q0 ... -q4) I noticed an
enormous CPU load with -q4 (sinc) but couldn't hear any differences in
audio quality. -q0 sounds as good as -q4.
Now my question:
When the audioadapter has to resample to the same frequency (from 48000
to 48000), do higher -q settings improve the audio quality? As I
understand there is no interpolation needed at all so -q0 would be
enough to have a perfect audio quality.
Any comments/ideas to this?
Interpolation will be needed when the clocks drift.