On 11/16/2016 04:17 PM, Tino Mettler wrote:
> Hi,
>
> I try to get bit-transparent playback/recording of a stereo stream with
> a RME 9632 card.
>
> My test setup the card clocked at 48 kHz and the AES input and output
> looped.
Which means you connected the digital output to the digital input I guess?
> When I tried to use pure alsa, I recorded 10 channels to get channels 9
> and 10 which is the AES input (I wasn't able to find a way to record
> only channels 9 and 10). However, I'm not able to play back anything
> during the recording. I get the error message "set_params:1361: Unable
> to install hw params".
Do you count "channel 9 and 10" one or zero indexed? :)
Here is the channel mapping from the source for reference:
static char channel_map_H9632_ss[HDSP_MAX_CHANNELS] = {
/* ADAT channels */
0, 1, 2, 3, 4, 5, 6, 7,
/* SPDIF */
8, 9,
/* Analog */
10, 11,
/* AO4S-192 and AI4S-192 extension boards */
12, 13, 14, 15,
/* others don't exist */
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1
};
>
> I also tried jack and started jackd this way:
>
> $ jackd -R -d alsa -d hw:DSP -z none -M -H
>
> I was able to play back a square sample and record channels 9 and 10
> using jack_rec. However, the result looks like it went though bad AD/DA
> conversion: jumpy edges and the linear parts unclean, too.
Depending on what you "mean" with "the result" this looks perfectly fine
to me. To be expected of a sampled square wave signal.
How did you generate the signal?
How did you measure/visualize the output?
Keep in mind, that with a limited sample rate, you will always have an
approximated square wave, looking exactly as you described: rippled
linear parts and jumpy edges. This has nothing to do with a loss of
quality in the digital domain.
If you want to check bit transparency, you need to compare the samples
of your digital input and output.
>
>
> I'll try to find out if the playback or recording part is the culprit.
>
> However, I'd like to get some comments if bit-transparent
> playback/recording can work at all with my setup. If it does, I'd
> appreciate to get some hints how to achieve this.
I don't see any reason why it would not work if you connect the digital
output to the digital input.
>
>
> Regards,
> Tino
>
Greetings
Markus
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