TX noise under Linux

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TX noise under Linux

magun
Hi all

I am using a RXTX6.3 alike SDR with 2 PCI sound cards and noticed the following problem under Linux:

When using the following Sound card allocation:

name_of_sound_capt = "alsa:Realtek"      # IQ in
name_of_sound_play = "alsa:C-Media"    # audio out
sample_rate = 48000

microphone_name = "alsa:C-Media" # mic  capture
mic_sample_rate   = 48000
mic_channel_I       = 0
mic_channel_Q     = 0

name_of_mic_play  = "alsa:Realtek" # mic I/Q
mic_playback_rate = 48000
mic_play_chan_I    = 0
mic_play_chan_Q   = 1

I find that after approx. 2 minutes the play back errors increase steadily with time. This is unnoticeable when receiving. However, after the play back error starts increasing, the transmitted signal suffers from short glitches that can be heard on a test receiver and noticed on a spectrum analyzer. This problem does not occur when sound_play and sound_capture uses the Realtek and the mic channels are allocated to the C-Media sound card.

This problem does not occur under XP.
         
Andreas
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Re: TX noise under Linux

ahlstromjc
Administrator
Hi,

I did not see this either.  It looks like a Linux audio problem; or possibly you are using a laptop with insufficient CPU power.  Try adjusting the audio tuning parameters in your config file.  If you can get any further info, please let me know.  I will try to test this after I finish my digital mode interface.

Jim
N2ADR
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Re: TX noise under Linux

Leigh L. Klotz Jr WA5ZNU
Administrator
In reply to this post by magun
Can you check .asoundrc and /etc/asound.conf to see if there is a
definition of Realtek that is using plughw or something similar that
interposes sample rate conversion?

You might try directly using "hw:0" and "hw:1" (assuming that's what
aplay -l lists these as).

Leigh/WA5ZNU

On 03/29/2012 08:08 AM, magun [via quisk] wrote:

> Hi all
>
> I am using a RXTX6.3 alike SDR with 2 PCI sound cards and noticed the
> following problem under Linux:
>
> When using the following Sound card allocation:
>
> name_of_sound_capt = "alsa:Realtek"      # IQ in
> name_of_sound_play = "alsa:C-Media"    # audio out
> sample_rate = 48000

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Re: TX noise under Linux

magun
Hi Leigh

I am using Ubuntu 10.04 - there is no .asoundrc or /etc/asound.conf file.

I noticed that pulse audio was running and removed it. Using the hw-identifiers according to aplay did not solve the problem

I am wondering if I have to generate a .asound.rc file and which parameters to fill in. A search on the internet regarding the use of 2 sound cards did not help. Could you please point me to the right information.

Andreas
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Re: TX noise under Linux

Leigh L. Klotz Jr WA5ZNU
Administrator

Andreasw,
I don't think you need to create an soundrc file.  I was worried one had been created defining a plugin that did some unwanted sample rate conversion but that is not the case.  Using 2 sound cards is nothing unusual for alsa and as far as I can tell you are doing that part right. 

Leigh/WA5ZNU

On Mar 31, 2012 11:26 AM, "magun [via quisk]" <[hidden email]> wrote:
Hi Leigh

I am using Ubuntu 10.04 - there is no .asoundrc or /etc/asound.conf file.

I noticed that pulse audio was running and removed it. Using the hw-identifiers according to aplay did not solve the problem

I am wondering if I have to generate a .asound.rc file and which parameters to fill in. A search on the internet regarding the use of 2 sound cards did not help. Could you please point me to the right information.

Andreas



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Re: TX noise under Linux

magun
In reply to this post by Leigh L. Klotz Jr WA5ZNU
Hi all

Thanks for your suggestions. It seems that the problem is not related to the CPU power as it also occurs on my desktop with an Athlon II 250 cpu.

I found out (on my desktop) that when the microphone capture is disabled the play back errors stay 0 and the TX signal is clean.

I installed a third sound card (USB) and used its input as microphone capture device. The problem was there again. Changes in latency did not help either. What other audio parameters could I fiddle with?

Andreas
I
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Re: TX noise under Linux

magun
With quisk-3.6.1,  the problem described at the beginning of this thread has disappeared also under Linux.
Thank you for fixing it and also the adjustment of the image sideband suppression.

Andreas