JackAudio June 2016

jackaudio@lists.linuxaudio.org

8 participants
6 discussions

[Jack-Devel] fractional frame rates for alsa_in and alsa_out

by Markus Grabner

Hi! A while ago I initiated work on a Linux driver for Line6 devices (now under sound/usb/line6 in the Linux kernel tree). Some of these devices have weird sample rates (39062.5Hz, derived from the 10MHz USB clock divided by 256). The alsa_in and alsa_out jack clients are convenient tools to use such Line6 devices together with more standardized hardware operating at, e.g., 48kHz. However, alsa_in only supports integer sample rates, and even after a couple of minutes, alsa_in doesn't detect the correct resampling factor 1.2288 (48000/39062.5), but still reports the initial approximated value 1.228816 (48000/39062). Admittedly, the error isn't too big, but is larger than the error of high-quality crystal oscillators. And, after all, why use an approximation if we know better? I modified alsa_in and alsa_out such that they accept a sample rate in floating point format (command line option "-r") and query the fractional sample rate from the ALSA driver to compute the initial estimation of the resampling factor (see attached patch). What do you think about this patch? Kind regards, Markus

8 years, 2 months

[Jack-Devel] netJACK2 with two nodes

by xan

Hello JACK community, I’m planning my new audio editing setup (both hard- and software) and before investing in hardware, I’d like to ask for advice. Here’s what I want to do: – Both computers run Linux. – On Computer A, I can browse the web and see Youtube videos, I can listen to MP3 files with Totem and I can do DAW stuff with Ardour. – Computer B does nothing more than getting all the sound output from A and feed it to the speaker through it’s soundcard. Here’s my theoretical approach: – Both computers run JACK. – A runs PulseAudio in top of JACK. – A runs with the net backend using netJACK2. – B has the Net Manager loaded which gets the audio from A and pipes it to the soundcard. – Every time I boot the two computers, they are ready to work. No daemons I have to launch manually, etc. I want the configuration to be done one time for all. I got my understanding of JACK through the network from here: https://github.com/jackaudio/jackaudio.github.com/wiki/WalkThrough_User_Net… And this site would also be my guide for setting up the thing. But I’m not a JACK expert at all. It’s the first time I’m doing something like this. So I want to make shure I got the basics right. And, maybe you now even a better step-by-step tutorial which does exactly what I want. So, I appreciate any comments on this. Bye, xan

8 years, 2 months

[Jack-Devel] [patch] Fix bug with alsa_in/alsa_out latency

by Xavier Mendez

Hello, Here's a quick fix for alsa_in and alsa_out, which currently set the playback latency of their ports to the target delay, but forget to convert this delay to JACK frames. See PR for more info. https://github.com/jackaudio/jack2/pull/215 https://github.com/jackaudio/tools/pull/8 Also convert the result of jack_frames_since_cycle_start() into ALSA frames, before subtracting it from the delay for the controller. Note that this change only has effect if ALSA and JACK sample rates differ, otherwise the behavior stays the same. Xavi

8 years, 4 months

[Jack-Devel] Suggestion for two new tools

by Xavier Mendez

I'd like to suggest two new tools. I find myself using them frequently whenever I'm dealing with sets of outputs / inputs of different latencies, or sometimes when I'm using software that adds noticeable (i.e. >= 15ms) latency. I think it would be best to add them as standard JACK tools because: - They perform a very basic task. - JACK has almost no latency-related tools AFAIK. - They demonstrate the power of JACK's latency API and could serve as [non-trivial] examples for devs trying to understand it. What do you think? I've attached a patch with both tools. If they get included, I'll write documentation about its usage and the latency API in general. Below is a summary of what they do: ## jack_lsync Synchronizes a set of ports for playback or capture, by inserting appropriate delays to compensate for latency. Example: Suppose you have one output `playback_1` with 20ms output latency, and another output `playback_2` with 50ms output latency: jack_lsync -a2 & jack_connect lsync:output_1 playback_1 jack_connect lsync:output_2 playback_2 lsync will insert a 30ms delay on the first output, giving you two outputs of 50ms latency. Instead of connecting to the original outputs, you'd connect to `lsync:input_1` and `lsync:input_2` respectively. ## jack_lset Corrects the reported latency of a port. Example: to increment the playback latency of `port` by 30ms: jack_lset 30ms & jack_connect lset:output_1 port Then connect everything to `lset:input_1` instead of `port`. Clients should ideally set the correct latency at their ports, or provide an option (as with -I and -O) for users to set them. This is not the case in practice, and there are also a number of legitimate reasons why users may want to correct latency externally.

8 years, 4 months

[Jack-Devel] shm registry full errors

by marcin＠saepia.net

Hello, at some point I am getting the following errors from JACK Jun 9 11:57:19 001-can1-plumber jackd[21110]: shm registry full Jun 9 11:57:19 001-can1-plumber jackd[21110]: Cannot create shared memory segment of size = 422 Jun 9 11:57:19 001-can1-plumber jackd[21110]: JackShmMem::new bad alloc Jun 9 11:57:19 001-can1-plumber jackd[21110]: Cannot open client Jun 9 11:57:19 001-can1-plumber jackd[21110]: Cannot create new client Max locked memory for this process is set to 134217728 while launching JACK via systemd. It effectively causes JACK to hang. I am using 1.9.10 (commit 1ed50c92) on ubuntu 16.04. The configure flags are --clients=500 --ports-per-application=4 (I am not reaching 500 clients limit when that occurs, they are around 250). JACK is started with dummy driver, and --port-max set to 2000. What is the reason for hitting SHM limit? Can I overcome this in any way? m.

8 years, 4 months

[Jack-Devel] Segfaults if setting --clients=512

by marcin＠saepia.net

Hello, I am compiling JACK2 from commit 7de15e7a (the same as shipped with Ubuntu 14.04). I need to set --clients to quite high value, and I have found out that setting --clients=512 causes jackd to segfault while --clients=500 is fine. Is that a bug or limitation by design? Marcin

8 years, 4 months

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JackAudio June 2016