Yet more info, the output of snd_pcm_hw_params_dump and snd_pcm_sw_params_dump (they look the same for both capture and playback): ACCESS: RW_INTERLEAVED FORMAT: FLOAT_LE SUBFORMAT: STD SAMPLE_BITS: 32 FRAME_BITS: 64 CHANNELS: 2 RATE: 48000 PERIOD_TIME: (666 667) PERIOD_SIZE: 32 PERIOD_BYTES: 256 PERIODS: 2 BUFFER_TIME: (1333 1334) BUFFER_SIZE: 64 BUFFER_BYTES: 512 TICK_TIME: 0 tstamp_mode: NONE tstamp_type: MONOTONIC period_step: 1 avail_min: 32 start_threshold: 32 stop_threshold: 1073741824 silence_threshold: 0 silence_size: 1073741824 boundary: 1073741824 > -----Original Message----- > From: Robert Bielik > Sent: den 15 januari 2018 17:47 > To: Robert Bielik <Robert.Bielik@xxxxxxxxx>; alsa-user@xxxxxxxxxxxxxxxxxxxxx > Subject: RE: Strange i/o problem > > Ah, forgot to mention a couple of things, this is on a Raspberry Pi 3 with > Raspbian Stretch, the rendering thread is set to SCHED_RR with max priority, > the timing of the callback is typically (in microseconds): > > min, mean, max, stddev: 655, 666, 680, 1.45639 > min, mean, max, stddev: 656, 666, 680, 1.25471 > min, mean, max, stddev: 640, 666, 694, 1.83335 > min, mean, max, stddev: 619, 666, 713, 2.10409 > min, mean, max, stddev: 656, 666, 681, 1.32999 > min, mean, max, stddev: 652, 666, 682, 1.65541 > min, mean, max, stddev: 651, 666, 685, 1.49302 > min, mean, max, stddev: 656, 666, 680, 1.33093 > min, mean, max, stddev: 649, 666, 690, 1.6246 > min, mean, max, stddev: 656, 666, 679, 1.3234 > min, mean, max, stddev: 656, 666, 680, 1.36177 > min, mean, max, stddev: 611, 666, 704, 1.9551 > min, mean, max, stddev: 651, 666, 687, 1.37784 > min, mean, max, stddev: 650, 666, 689, 1.4738 > min, mean, max, stddev: 609, 666, 722, 2.2253 > min, mean, max, stddev: 656, 666, 680, 1.57805 > min, mean, max, stddev: 643, 666, 683, 1.54424 > > (which to me looks more than OK) > > > -----Original Message----- > > From: Robert Bielik [mailto:Robert.Bielik@xxxxxxxxx] > > Sent: den 15 januari 2018 17:41 > > To: alsa-user@xxxxxxxxxxxxxxxxxxxxx > > Subject: Strange i/o problem > > > > I have a strange problem: I'm trying to pipe audio input -> output using a > I2S > > device @48000 Hz and 32 frames buffer size and 2 periods, to get as low a > > latency as possible. > > > > It works nicely if I either: > > 1. Use capture + playback and record capture to a wav file (sounds fine). > > 2. Use playback only and generate sine waves. > > 3. Pipe capture -> playback with a larger buffer size, such as 64. > > > > But if I have capture + playback, I get a very strange output noise akin > > towards heavy intermodulation distortion. > > > > The rendering thread is (pseudo code): > > > > while (true) { > > if(capture_active) { > > snd_pcm_wait(capture_handle, timeout); > > read_pcm_data_into_buffer(capture_handle, input_buffer); > > } > > do_callback(input_buffer, output_buffer); > > if (playback_active) { > > snd_pcm_wait(playback_handle, timeout); > > write_pcm_data_from_buffer(playback_handle, output_buffer); > > } > > } > > > > Any ideas what can go wrong ? > > /R > > > > > > ------------------------------------------------------------------------------ > > Check out the vibrant tech community on one of the world's most > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Alsa-user mailing list > > Alsa-user@xxxxxxxxxxxxxxxxxxxxx > > https://lists.sourceforge.net/lists/listinfo/alsa-user ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
