And as also said earlier, I don't believe very much that it will work that easily, since the CPU clock is a) worse than the typical SDR and sound card clocks, b) has different resolutions, c) and needs to still be sufficiently interpolatable for the jittery, variable-workload-length that GNU Radio has. The point c) is what's different for Jack internally, because that can work on fixed-length buffers.
This is a comment that you've gotten from me (and by the way, Fons, too) multiple times now. Could you maybe elaborate how you're planning to solve all a),b),c) instead of asking for new feedback? Best regards, Marcus On 09/26/2017 06:20 PM, Benny Alexandar wrote: > Hi Marcus, > > As said earlier there is no true clock as such. We need to rely on CPU > clock and measure the deviation. The reference clock is the > transmitter time duration between two symbols which is a preset value. > Do you have any suggestions for a *better reference clock* > > -ben > > -------------------------------------------------------------- > > Hi Benny, > > you're, again, missing the core problem: it's hard to measure the time > deviation between two symbols without a better reference clock. And > you don't have that. And thus, we're back at the start of all our > email chain. > > Best regards, > > Marcus > ------------------------------------------------------------------------ > *From:* Benny Alexandar > *Sent:* Tuesday, September 26, 2017 10:56 PM > *To:* Marcus Müller; GNURadio Discussion List > *Subject:* Re: [USRP-users] Audio Control loop testing > > Hello, > > Now the timing of input side is after detecting the start of symbol. > Every symbol will be timestamped and measure the time deviation > between two symbols. > > d = t1 - t0, > where t0 - time of arrival of symbol (n) > t1 - time of arrival of symbol (n+1) > d - time deviation between two symbols. > > D - time duration between two symbols according to digital radio > standards, then error = ( D / d ) - 1 > > Please send your suggestions feedback regarding this approach. > > -ben > ------------------------------------------------------------------------ > *From:* Benny Alexandar > *Sent:* Friday, September 22, 2017 10:26 PM > *To:* Marcus Müller; GNURadio Discussion List > *Subject:* Re: [USRP-users] Audio Control loop testing > > Hi Marcus, > > Please find the attached figure on how the audio control loop will be > placed in > Gnu Radio chain. In the figure the first block is the RF IQ > acquisition block which samples the RF samples and put a timestamp. It > is then passed on to channel and audio decoder and finally reaches > the audio sink. Audio sink does the audio playback on fragments of audio. > > The audio control loop module has two inputs and one output. The > inputs are for sending the timestamp of write side and read side. In > this case write side is RF capture and read is from audio sink. Note > these two time stamps are coming from different clock, the RF capture > uses PC CPU clock where as the audio sink has sound card clock. The > output of audio control loop is used to control the re sampler which > sits in between audio decoder and audio sink.More details on how the > audio control loop will be send soon. > > Please send your feedback regarding this approach. > > > -ben > ------------------------------------------------------------------------ > *From:* Marcus Müller <marcus.muel...@ettus.com> > *Sent:* Tuesday, September 19, 2017 10:47 PM > *To:* Benny Alexandar; GNURadio Discussion List > *Subject:* Re: [USRP-users] Audio Control loop testing > > > Hi Ben, > > >> May I know why not with JACK ? > > From the very same email you're referring to: > > >> (not much sense writing it for the Jack sink, if Jack can already do >> it internally) > Also, >> Here, I need your inputs. > I spent around 5 hrs on input on this topic already. I don't feel like > you need more input, it feels more like you haven't had the chance yet > to understand all the input that there is on the GNU Radio mailing > list. We should also not be having this discussion on usrp-users, as > your approach doesn't involve USRPs directly! > >> Can you please state the requirements. How it has to be in GNU radio >> chain etc. > > Please re-read my previous email. I explicitly say I'm not even > convinced this will reliably work in software. GNU Radio is software. > What about you just start by trying to implement a control loop, and > read as much on theory of discrete-time control systems as you'll need > for this? I'm afraid I can't take that burden off your shoulder if you > want to implement a control loop. It is hard stuff. > > Best regards, > Marcus > On 09/19/2017 10:10 AM, Benny Alexandar wrote: >> Hi Marcus, >> >> Yes its true I couldn' t make much progress on this. Not able to >> find time as I have a full time job. If I remember correctly, you >> mentioned that no-one has implemented audio control loop within GNU >> Radio. And you were suggesting to write it for ALSA and not with JACK. >> >> May I know why not with JACK ? If I need to make it with JACK, GNU >> radio should run as a client and output to JACK input port and >> another client which does the audio control loop and send the output >> for playback. May be its not required, if we can make a sink block >> with ALSA and implement the audio control loop. >> >> Here, I need your inputs. Can you please state the requirements. How >> it has to be in GNU radio chain etc. >> >> -ben >> >> ------------------------------------------------------------------------ >> *From:* USRP-users <usrp-users-boun...@lists.ettus.com> on behalf of >> Marcus Müller via USRP-users <usrp-us...@lists.ettus.com> >> *Sent:* Tuesday, September 19, 2017 2:10 AM >> *To:* usrp-us...@lists.ettus.com; GNURadio Discussion List >> *Subject:* Re: [USRP-users] Audio Control loop testing >> >> >> Hi Ben, >> >> >> that's the old multi-clock problem we've been talking about multiple >> times – it's hard to even define what the "correct" clock is, so you >> usually just settle on recovering the transmitter clock and, if you >> were doing this in hardware, would derive the audio DAC's clock from >> that. >> >> In a software receiver, you need to estimate the offset of the audio >> DAC clock from the sender's audio clock. That's hard to do properly, >> because these clock offsets might be to fine to do it with general >> purpose PC CPU software. But we've talked about all that before on >> the Discuss-gnuradio list! >> >> >> As a way around that, you might use the same clock to derive the RF >> receiver's sampling clock and the audio DAC's sampling clock. You >> then get a direct relation between RF sampling and audio playback, >> for example "every 1 million RF samples, I need to produce one audio >> sample". Fons and I really tried to explain that in about 20 emails >> on discuss-gnuradio. So, I think we've covered the stage of "any >> suggestions on this would be helpful" pretty well. It is a hard >> problem, and there's a solid chance you can't solve it for all use >> cases in software. There's also a solid chance you might be able to >> solve it for a specific use case, but that would require you to >> become an expert on multi-rate processing and clock matching, and >> frankly, you're not showing much progress at that over last 10 months. >> >> >> Best regards, >> >> Marcus >> >> >> >> On 09/16/2017 05:38 AM, Benny Alexandar via USRP-users wrote: >>> Hi, >>> >>> I want to create an artificial audio drift in transmitter side and >>> test it using my audio control loop in receiver. This is what I'm >>> planning. >>> >>> Take an audio wav file which is sampled at 12 kHz. Re sample it such >>> that the sample rate is now having a drift of 100 ppm, ie with >>> sample frequencies with an error up to 12000*100e-6 is 1.2Hz in case >>> of 12kHz sample frequency. Now transmit this audio file using Gnu >>> radio and USRP. >>> Receiver does the channel decoding and audio decoding. >>> So in this most extreme case the receiver drifts with more than one >>> sample per second, so after an hour it is drifted by 1.2*3600 = 4320 >>> samples >>> >>> If the receiver doesn't have an audio control loop then it will go >>> into under run. By enabling the audio control loop i can check the >>> drift compensation. >>> >>> Any suggestions on this method of testing. >>> >>> -ben >>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> usrp-us...@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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