> From: Jean-Michel FRIEDT > Date: Thu, 19 Jul 2018 16:17:10 +0200
> Indeed I have since checked any source of crosstalk and removed all links from > source to audio sink but the one going to input number 3 and still the same > issue is observed. However remplacing 90000 Hz output (at 192000 Hz sampling > rate) with 90000.1 Hz solves the issue of the unexpected shape at the output > of the sound card. It seems to me we have a strange relation when incrementing > the NCO phase, but I fail to identify the cause of the problem, and why > moving the frequency as the flowgraph is running solves the output shape. > I thought that incrementing and decrementing the frequency defined as a > > floating point number might lead me to a value slightly different from 90.0 > kHz, > [snip] > On Thu, Jul 19, 2018, 4:49 AM Jean-Michel FRIEDT < > address@hidden> wrote: [snip] > When first launched with an output frequency set to 90 kHz, the sound > card > output looks like jmfriedt.org/snd1.png, ie with some spectral > component > around 6 kHz whose origin I am unable to identify. If, using the > slider, I > change the frequency and set it back to its original value of 90 kHz, > I get > the fine output of jmfriedt.org/snd2.png which looks as good as I can > expect from an output frequency so close to the Nyquist frequency. [snip] Having the benefit of hindsight, I'll guess it is a beat frequency, since GCD(192000, 90000) = 6000. If a QT Freq Sink (with 8192 points and a Kaiser window) doesn't show the 6 kHz component, I'd blame the sound card. -Andy _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
