Re: [Discuss-gnuradio] Timestamping baseband samples

[Marcus Müller]

Hi ben,

the Ettus USRP series of devices (N2x0, B2xx, E3xx, X3xx, N3xx) have RX
sample time stamping that you can find as tags in your sample flow.

That means they can annotate a sample buffer with the device time of
the first contained sample. The device time can be set according to an
external standard, if helpful (e.g. a GPS clock).

You won't find anything surprising in there: The first received item
will have a tag containing the device time at which that sample was
received. From there on, you can use (sample number)/(sampling rate) to
calculate the device time corresponding to each packet. Since absolute
time doesn't matter to your application, you could just as well do
without that tag and simply count samples. With the timestamps, you
still count samples, and add the timestamp from the first sample.
There's no additional information that helps you solve the two-clock
problem to be gained here.

Best regards,
Marcus

On Sat, 2018-02-10 at 07:06 +0000, Benny Alexandar wrote:
> Hi All,
> 
> In Broadcast receiver where the RF samples are received on AIR and
> channel decoder does the demodulation of digital radio symbols, and
> extracts the compressed audio data. This is then fed to an audio
> decoder to decode the audio. After decoding the uncompressed audio
> has to be played out. 
> I would like to implement the jitter buffer, by having time stamps.
> So my question is where to do the timestamping, the timestamp put
> after audio decoding will be jittery because of variable audio
> content and compression effects. So the best place is to put at the
> RF input when baseband samples are buffered using DMA, this then can
> be corrected for clock recovery and use it while sending out audio.
>   
> 
> Any suggestions on this approach.
> 
> -ben
> 
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