ALSA_IO(1)

🎀 ALSA_IO 🎀

okay bestie, this is the ALSA_IO page from the General Commands Manual and it's giving main character energy 💅✨

✨ NAME ✨

so the name section says these are alsa_in and alsa_out, Jack clients that do I/O with an alternate audio interface 🦋

💅 SYNOPSIS 💅

alsa_in [options]
alsa_out [options]

🌸 DESCRIPTION 🌸

okay so a JACK client is basically a little helper that opens a specific audio interface (one that's different from the one the JACK server is using, if there even is one 👀) and shuttles audio back and forth between its JACK ports and that interface. alsa_in gives you data from the interface (potentially for capture), and alsa_out sends data to it (for playback) 🎧

the audio interface used by alsa_in/alsa_out doesn't have to be synced with the JACK backend (or the hardware it's using) 🙈 instead, it tries to resample the output stream to make up for drift between the two clocks. ✨

as of jack-0.116.3 this works almost perfectly 😭 it just takes some time to reach absolute resample-rate stability, so give it some minutes (it's intended to run permanently anyways) 💜

🎀 OPTIONS 🎀

• -j jack_client_name — set the client name 💖
• -d alsa_device — use this soundcard 🔊
• -v — verbose mode! prints out the resample coefficient and other useful debugging params every 500ms, and also reports soft xruns 📣
• -i — instrumentation 🧪 logs the 4 important params of the samplerate control algorithm every 1ms. you can pipe it into a file and plot it. this is only needed if it's not working as expected and we need to tweak some obscure params. find me on irc.freenode.org in #jack to set it up correctly 🫶
• -c channels — set the number of channels 🎶
• -r sample_rate — set the sample rate. the program resamples as necessary, so you can connect a 44100 jackd to a soundcard that only supports 48000 🌈 (default is the JACK sample_rate)
• -p period_size — set the period size. it's not related to the jackd period_size, but sometimes it affects the quality of the delay measurements 🧚 setting it lower than the jackd period_size only works if you use a higher number of periods
• -n num_period — set the number of periods. see the note for period_size ⭐
• -q quality — set the resampler quality from 0 to 4. it can significantly reduce CPU usage 🍓
• -m max_diff — the value at which a soft xrun occurs. basically the window in which the dma pointer may jitter. the author doesn't think you need to play with this anymore 🙈
• -t target_delay — the delay alsa_io should try to approach. same deal as max_diff. it gets set up based on -p and -n, which is generally sufficient 💜
• -s smooth_array_size — controls the size of the array used for smoothing the delay measurement. its default is 256. if you use a pretty low period size, you can lower CPU usage a bit by decreasing this, but most CPU time is spent in the resampling, so it won't be much 🧮
• -C P — Control Clamp 🪄 if you have a PCI card, the default value (15) is too high for -p64 -n2... setting it to 5 should fix that.

be careful! setting this too low lets the HF noise on the delay measurement come through onto the resamplerate, which might degrade output quality. (but it's a threshold value, chosen to mask the noise of a USB card, whose amplitude is 50 times higher than a PCI card's, so 5 won't lose you any quality on a PCI card) ⚠️

• -S server_name — the server to connect to. this lets you attach to a named jack2 server 🖥️

👑 AUTHOR 👑

Torben Hohn 💖

that's the whole page, bestie 🫶 it's from page 4 of the footer, dated 2022 🌸 slay forever 💅✨