Re: [Discuss-gnuradio] Waveform after AM demodulation looks weird

[Anton Komarov]

Marcus, w/o AGC audio sometimes is creapy. I have tested AGC2, tried to play with attack and decay, but at last when there is a plane in the vicinity dongle overloads and sound become very loud. Then i tested FAGC and it fits well! 1024M/64 gives 16k and 256 samples equals - 62 ms of signal. Works ok for me.

On Fri, Apr 25, 2014 at 7:25 PM, Marcus Müller <address@hidden> wrote:

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Actually I'm a little confused - Is seeing an AGC in an AM demodulator
something you usually do?
Especially the feedforward AGC should be rather err jumpy with a scope
of but 256 samples, unless I'm missing something; f_sample seems to be
1024ksps, thus 256 samples max search and rescaling should behave very
badly if there are baseband signal contents below 4kHz -- and that
should be the case for audio, usually?

Greetings,
Marcus

On 25.04.2014 16:03, Marcus Leech wrote:
> An AM demodulator is a squaring function.  It can only *ever*
> produce positive values.  You can remove DC offset by using a

> high-pass filter after it. on Apr 25, 2014, *Anton Komarov*

> <address@hidden> wrote:
>
> But when we have only positive values that means in fact we have
> 0.5 DC offset, and that is bad. Moreover i've made test recording
> with GQRX - waveform is fine! Looking into the code, nothing
> special, am demod->low-pass->wav-sink.
>
> -- public PGP key http://pastebin.com/dqZqgyVE
>
>
> On Fri, Apr 25, 2014 at 5:11 PM, Michael Ossmann <address@hidden

> <mailto:address@hidden>> wrote:
>
> On Fri, Apr 25, 2014 at 04:14:30PM +0400, Anton Komarov wrote:
>>
>> Hi, you can find in attach AM demodulator grc file. Everything
>> is straight forward with demod but audio file generated looks
>> weird. Only positive values of amplitude.
> The particular definition of "amplitude" adopted by GNU Radio (and
> pretty much everyone else in SDR as far as I know) is "absolute
> value". It is correct for it to always be positive.
>
>

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