Re: [Discuss-gnuradio] [GSoC 17] DAB: updates of the week

[John Ackermann N8UR]

Hi Biju --

I was mainly asking whether Benny had a proof of concept for his 
suggested approach.  I understand about resamplers.

The thought in my mind, though I don't know if I have the skills to 
implement it, is a block placed immediately before the audio sink that 
provides a buffer and measures whether it is filling or emptying over 
time.  That information drives a feedback loop that adjusts a rational 
resampler on the input side of the buffer to keep the buffer level 
constant, thus correcting for clock errors.  As shown in terrible ASCII art:

                          Nominal 1:1
Audio-rate samples --> Rational Resampler --> Buffer --> Audio Sink
                               ^                v
                               |                |
                               ^----------------<
                           (Adjust Int/Dec values to
                          maintain buffer at 50% full)

I know that block doesn't currently exist, but might be an awfully 
useful thing to have.

John
----
On 06/07/2017 12:23 PM, Biju Ravindran wrote:
> Hi John,
>
> I'm not aware of any gnu radio blocks available for audio synchronization.
>
> However, you're asking about resampling: Well, resamplers do exist :) !
>
> We've got a totally different problem, though: To resample properly,
>
> you'd need to know (or better: estimate) the clock error.
>
>
>
> On Wed, Jun 7, 2017 at 2:47 AM, John Ackermann N8UR <address@hidden
> <mailto:address@hidden>> wrote:
>
>     Hi Benny --
>
>     As I mentioned in another message, I'm struggling with the RF-audio
>     interface now.  Do you have any example code for your suggestion
>     that I might play with (in my mind, the idea would be an "audio
>     synchronizer" block that would take input at the nominal audio rate
>     and output at the actual rate, correcting for clock error to keep
>     the stream flowing smoothly).
>
>     If a prototype exists, I'd be happy to plug it into my current app
>     to see what happens.
>
>     John
>     ----
>
>
>     On 06/06/2017 12:02 PM, Benny Alexandar wrote:
>
>         Hi Luca,
>
>
>         Nice to see your progress so far. Once you have the
>         DAB receiver audio listening in place, I would
>         suggest to have an audio synchronization for continuous
>         playback without any buffer overflow or under-runs.
>
>         DAB+ audio super frame length is 120ms according to DAB+
>         standard (ETSI TS 102 563). Each audio super frame is
>         carried in five consecutive logical DAB frames.
>         Which means 120ms of audio is mapped to 5 DAB frames.
>
>         If I add a timestamp at the receiver when the first DAB frame
>         sample arrives, I can check the max latency when it comes to
>         audio renderer, I mean after buffering to adjust the variable
>         decoding time of compressed audio.
>
>         t_D = t_A -  t_B ,
>         where,
>          t_A = time at audio out
>          t_B = time at input baseband sample.
>          t_D = maximum system delay.
>
>         The difficulty is to estimate the slow clock drift correctly
>         and separate it from the short-time channel/decoding jitter.
>
>         Add a delay to buffer audio at audio out, say  D, which is larger
>         than max system delay. Whenever the audio reaches audio out,
>         check the
>         delay to separate the clock drift.
>
>              drift = t_D - D
>
>         Please let me know if you need any more details.
>
>         -ben
>
>
>
>
>
>
>
>
>
>
>
>         ------------------------------------------------------------------------
>         *From:* Discuss-gnuradio
>         <address@hidden
>         <mailto:address@hidden>> on behalf of
>         Moritz Luca Schmid <address@hidden
>         <mailto:address@hidden>>
>         *Sent:* Friday, May 26, 2017 6:19:31 PM
>         *To:* GNURadio Discussion List
>         *Subject:* [Discuss-gnuradio] [GSoC 17] DAB: updates of the week
>
>
>         Hi everyone,
>
>         I just published my latest updates of my DAB project in a new
>         blog post
>         <https://dabtransceiver.wordpress.com/
>         <https://dabtransceiver.wordpress.com/>>.
>
>         This week, I created a source block for the Fast Information
>         Channel and
>         started to build a reception chain for the Main Service Channel
>         (where
>         the audio data is transmitted).
>
>         Read more about it in my post.
>
>
>         Cheers
>
>         Luca
>
>
>
>         _______________________________________________
>         Discuss-gnuradio mailing list
>         address@hidden <mailto:address@hidden>
>         https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>         <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio>
>
>
>     _______________________________________________
>     Discuss-gnuradio mailing list
>     address@hidden <mailto:address@hidden>
>     https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>     <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio>
>
>
>
>
> --
> Regards,
> Biju Ravindran