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Latency Correction

Hi There,

I have been getting into doing music recordings at home and have been primarily using Audacity so far, but it has no real midi implementation, and as I have been getting more midi keyboards, it is good to be able to do some sequencing.

I decided to learn qTractor as my software as it has a nice interface and is easy to use. A lot of the other programmes have too many features for me, ones I don't really need.

I was wondering if it is possible to do automatic latency correction in qTractor, like it is in Audacity, to account for the latency in the sound card? In Audacity I create a click track, plug the line out jack into the line in jack and then push record and then compare the offset. Then I just adjust the latency offset compensation until they align acceptably.

I find that with using qTractor currently, when doing multi track recording, things tend to get slightly out of time with each other and it sounds like I can't keep in time (which I can usually as I play in a brass band). Also even when doing multi-track midi recordings (from hardware synths) things get out of time too.

Also is there any way to set it up so that it automatically creates a new audio track each time you record, like audacity does? This is really handy for doing multiple takes quickly, when doing vocals or acoustic instrumental parts.

Thanks very much for creating this amazing piece of software Rui, it is fantastic.

rncbc's picture

hi, thanks

yes, qtractor does have audio input latency compensation, as far as it's reported by the JACK sub-system.

however, it might not be always perfect or precise, mostly depending on your specific soundcard device (USB is quite notoriously bad in this regard) and on the running JACK settings: as a rule of thumb, you should set JACK buffer-size to a bare minimum: 128 frames/period is good-enough for most purposes and prosumer-graded devices; for USB devices it's also highly recommended you're to set to a 48000 sample-rate, possibly on 3 periods/buffer.

if you can't run or start JACK reliably at that minimum sane specification, then you probably have one ugly and bad cheapo-graded device to begin with.; if you insist though, then abandon all hope on getting any real-time low-latency, precision multi-track recordings of any kind on qtractor... be that audio PCM or even MIDI:)...

when all's set and good(enough) as said above, you may need to adjust a few things and try on:

  • qjackctl > Setup > Settings > Advanced > Latency I/O: add some systemic input latency (in frames) in the same amount you would possibly need to adjust, on any previously recorded audio clip in qtractor (not audacity);
  • qtractor > View > Options... > MIDI > Playback > Queue timer (resolution) : make sure you select the high-resolution timer (hrtimer) or one with greater or equal resolution than 1000hz; also, try whether you get any acceptable results on keeping in time while recording MIDI, by enabling the MIDI queue time drift correction (or not).


Thanks, I was using an old MBOX 2 which I bought off Trademe (New Zealand version of eBay) for $16 NZD, but I managed to get a Lexicon Alpha interface for only $3 NZD off Trademe which had dirty pots which I cleaned, and with those settings it seems to be working fine.
I am very pleased with qtractor now, and have done a full recording using it. I just need how to learn how to mix a bit better and it should be complete!
Recording music is certainly lot more technical than just playing music.



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