rtl_fm problem with capture audio

[Ron Senykoff]

My experience was that several commands / examples I've seen gave me
stutters here on a pretty beefy computer. It took playing around and I
didn't document everything, but so far what I've got that 'works'
stutter-free, although maybe is not so great... but it does work anyways. I
know it isn't a rasbpi but it showed me that a lot of times it isn't the
hardware causing the stutters.

ron at tripel:~$ rtl_fm -W -f 96.9e6 -W -s 200000 -r 48000 - | aplay -r 48k -f
S16_LE -t raw -c 1
Found 1 device(s):
  0:  Generic, RTL2832U, SN: 77771111153705700

Using device 0: Generic RTL2832U (e.g. hama nano)
Found Rafael Micro R820T tuner
Oversampling input by: 2x.
Oversampling output by: 4x.
Buffer size: 5.12ms
Tuned to 97315000 Hz.
Sampling at 1600000 Hz.
Output at 48000 Hz.
Tuner gain set to automatic.
Playing raw data 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono





On Thu, Nov 29, 2012 at 1:28 PM, keenerd <keenerd at gmail.com> wrote:

> On 11/29/12, Pete Zaitcev <zaitcev at kotori.zaitcev.us> wrote:
> > But another thing is that rtl_fm just won't work until the signal is
> > strong enough.
>
> Maybe you should try increasing the gain.
>
> > Final command line was this:
> > rtl_fm -l 0 -f 99.5e6 -N -s 170e3 -o 4 -A -r 24e3 - | \
> > aplay -r 24k -f S16_LE -t raw -c 1
>
> Really, much smarter to use -W instead.  You are losing a moderate
> amount of the signal.  First, wbfm is slightly off center pushing 10%
> of the signal out of range.  Second, it carries audio information up
> to 16kHz and resampling at 24ks/s discards another 25%.
>
> rtl_fm -W -f 99.5e6 -g 49 | aplay -r 32k -f S16_LE -t raw -c 1
>
> will work better.  No reason to spell it out the long way.
>
> -Kyle
>
>
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