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Re: [Discuss-gnuradio] GNU Radio Companion - ALSA

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] GNU Radio Companion - ALSA
Date: Sun, 19 Feb 2017 15:48:35 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

You're right, we should tackle this more systematically.

My problem is that I don't have a RPi3 to play around with at hand, so I
have to trust you on the "HW:0,0"; it's not a very typical string,
through, as most alsa device names are lowercase. Could you share the
output of "aplay -L" with us?

Best regards,

On 19.02.2017 15:16, Robin A. Jensen wrote:
> Hello Marcus.
> Thanks for your reply and your welcomming to the community.
> I've made the changes as suggested.
> Also i've made a setup on a Windows 10 machine, to ensure the script
> runs.
> With the changes the sound is much better! :-)
> But when i run the same setup on RPi 3 / Jessie-distro i've end up
> with the same result, no matter what I do with the Audio sink.
> I'm using Gnu Radio Companion 3.7.5
> The error code is still:
> ALSA libpcm.c2239:)snd_pcm_open_noupdate) Unknown PCM HW:0,0 <-- 10
> times this line
> gr::log :ERROR: audio_alsa_sink0 - [HW:0,0]: No such file or directory.
> File "/home/pi/radio/top_block.py", line133, in <module>
>  tb= top_block()
> File "/home/pi/radio/top_block.py", line82, in __init__
> self.audio_sink_0 = audio.sink(48000, "HW:0,0", True)
> File "/usr/lib/python2.7/dist-packages/gnuradio/audio/audio_swig.py",
> line 195, in make
> return _ausio_swig.sink_make(*args, **kwargs)
> RuntimeError: audio_alsa_sink
> I know is alwayes is eassy to blame the software, but could it be a bug?
> As i said. i've tried with all the suggested lines from documentation
> of the block.
> Best regards
> Robin.
> Den 18-02-2017 kl. 18:17 skrev Marcus Müller:
>> Hi Robin,
>> first of all: Welcome to the GNU Radio community!
>> On 02/18/2017 05:29 PM, Robin A. Jensen wrote:
>>> Hello all of you.
>>> I've just recieved my RTL-SDR dongle and is all new to this sdr-stuff,
>>> so please bear over with me, if i'm at the wrong place.
>>> I'm using GNU Radio Companion on a RPi 3 and no mather what i'll do, i
>>> can't get the sound to work.
>>> If a'im using rtl_fm and aplay, i'll get sound but it won't set on the
>>> radiostation.
>> aha, so that's good, the sound system as it does work.
>> You'll probably want to use "aplay -L" to find the possible ALSA device
>> names that you can use in the GNU Radio Audio sink.
>>> I'll take on that later.
>>> I've createt a small FM Reciever in GNU Radio companion and everytime
>>> i'll execute the script i'll get an error:
>>> RuntimeError.audio.alsa.sink
>> Hm, I've never seen a GNU Radio error being printed like this; but that
>> might just be me. However, I can't reproduce this error printing shape
>> as hard as I try.
>>> I've been all over the internet to find a solution but with no luck.
>>> So now i'm have a hope that this mailling list can help me?
>> My suspicion is that your audio device doesn't like the sampling rate
>> your trying to use, or you need to specify a device name (or both). Can
>> you make things work on the PC you use to design these flow graphs?
>> I'd start with a signal source (sampling rate == the sampling rate that
>> you set in your Audio sink), configured to produce a "float" output sine
>> of 1 kHz, directly connected to an Audio sink. If that works, move on.
>> --------------------------------------------------------------------------------
>> What I say about the flow graph in the following has, as far as I can
>> tell, nothing to do with the error you're getting. Still, there's
>> mistakes in the flow graph that would make it impossible to successfully
>> run it, and thus I'd like to avoid frustration later on by pointing them
>> out know:
>> So, the main issue with your flow graph is that the sampling rate at the
>> audio sink must be what you configured your audio sink for (48 kHz).
>> But: that rate is the result of your SDR's sampling rate (2MS/s),
>> multiplied with all interpolations, divided by all decimations in the
>> path between.
>>> My setup is:
>>> RTL-SDR Source: samplerate:  2M, frequency 96.5 MHz ->
>>> Rationel Sampler: Interpolation 4, Decimation: 1 ->
>> Uh, that means that you have now 8MS/s. That seems unnecessary, since to
>> capture a <100 kHz wide FM channel, you wouldn't even need the 2MS/s
>> you get
>>> Low Pass Filter: Sample rate: 2M, Cutoff freq: 100K, Transition Width:
>>> 100k ->
>> Which contradicts the 2MS/s used here, so you're actually getting 400kHz
>> passband width, 400kHz transition width. Also, this feels like a prime
>> candidate for including decimation in the filter (because the resulting
>> bandwidth is 200 kHz (if you overlap the two transition widths), and for
>> that you'd only need 200 kS/s of complex digital signal).
>>> WBFM Recive: Quadrature: 500K, Audio Decimation: 1 ->
>> This is now off by a factor of 16; are you sure you should be using
>> "interpolation=4,decimation=1" instead of the inverse?
>>> Rationel Sampler: Interpolation: 500
>> Certainly not :) 8 MS/s · 500 = 4 GS/s
>>> Decimation: 48
>> Aside from that not even having greatest common denominator of 1 with
>> 500 (you can't know that this is important, not blaming you), this would
>> give you an output sampling rate of 4GS/s/48 = 1 GS/s / 12 = 83.333
>> MS/s. Which isn't even a multiple of 48 kHz, which you use in the audio
>> sink:
>>> ->
>>> Audio Sink: Sample Rate: 48 KHz, Device Name: HW:0,0
>>> I've found that recipie on a Hack5 video and there it's working
>> I think there's some error in the way you configured these resamplers. I
>> don't know the Video you're referring to, but the amount of rational
>> resamplers used here alone, paired with the fact that you don't decimate
>> in the WBFM receiver makes me kind of suspicious this might not have
>> been the optimal video to take reference designs from!
>> --------------------------------------------------------------------------------
>> Best regards,
>> Marcus
>>> With best regards
>>> Robin.
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