Re: [Discuss-gnuradio] Wav File Source and Audio Sink

[Marcus Müller]

Dear Igor,

can't point this out of enough:
> Signal Source (float, sine, 1khz freq, sample rate 8000) -> Throttle
> ->  Wav File Sink (sample rate 8000, 8 bit per sym).
Never, ever use a throttle block in a flowgraph where hardware dictates
the physical sampling rate.

Your GNU Radio companion should even have warned you about that, if your
GNU Radio version is rather recent:

> Generating: "/home/igor/top_block.py"
> >>> Warning: This flow graph contains a throttle block and another
> rate limiting block, e.g. a hardware source or sink. This is usually
> undesired. Consider removing the throttle block.
If you're not seeing aUaU... on the console, you're lucky. Usually, you
would have built a system with two competing clocks. One is *bound* to
be a little slower than the other, and if it's the throttle, your audio
sink would have no samples to play when it needs them.

I do, however, suspect that your sound system doesn't support a 8kHz
sampling rate. Try 44.1kHz, as it's supported by most systems.
If that doesn't help: try explicitely setting the ALSA device to use;
"aplay -L" will usually list all available output devices.

Also, try going down with the amplitude a bit. Typically, 0.4 as
amplitude is enough to drive sound cards "loud", and higher values often
result in clipping.

Best regards, and happy hacking,

Marcus

On 02/26/2015 09:08 PM, address@hidden wrote:
> Hi all,
>
> I am little bit puzzled by a simple flowgraph.
> I have prepared a wav file using following graph: Signal Source
> (float, sine, 1khz freq, sample rate 8000) -> Throttle ->  Wav File
> Sink (sample rate 8000, 8 bit per sym).
>
> Then i created graph for listening: Wav file source -> Audio Sink
> (sample rate 8000) + FFT Sink.
> And then i ran this flowgraph, i faced with following problem: I don't
> hear anything from audio sink.
>
> FFT sink shows me that data is coming, 1 khz peak is present on FFT,
> but i can't hear it.
>
> Could somebody explain this strange behaviour.
>
> Best regards,
> Igor
>
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