A few questions about latency compensation

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jcsa
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Right now I'm running jackd with 2 buffers * 64 frames. Ardour reports 1.3ms latency. I'm getting no xruns. Does this sound reasonable considering my hardware? I expected a higher buffer would be necessary?

With the jack settings I mentioned I'm getting synced audio when I multitrack, but if I use a higher buffer(for ex. 1024 ~20ms) there seems to be a noticeable delay between tracks, and between any track and the click track. I thought the latency set in jack would be automatically compensated for?

Second question, does latency compensation somehow recognize hardware latency? If so, how? I thought that would be something I would have to configure? I expected a lot of hardware latency because of my poor sound card, so it confuses me that any track sync delay I experience seems to be related to my jackd settings.

My setup:

-Onboard sound: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6 Family) High Definition Audio Controller (rev 03)
-3.0ghz pentium 4 ht
-1024MB ram 4*256 (2 dual channel kits)
-200GB 7200rpm sata HD

I'm recording one track at a time:

1 Audio-Technica Dynamic Mic > Tascam Portastudio 414 > Line In of sound card

I don't know much about digital recording so let me know if I'm talking crazy or misunderstand something. Thanks!

peder
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Joined: 2007-05-08
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I'd say you're lucky no get no xruns with 1.3ms on an Intel card (and usually I think they require 3 buffers to work OK as well).

About latency: The compensation is gathered from the jack setting. Ardour has no way of detecting the hardware latency but it uses the value it gets from jack and that value is calculated using the buffers and frames

The delay you're experiencing during higher settings is probably because you're using Ardour to monitor the sound you're recording. The latency is compensated for when putting the sound on disc (i.e it's timestamped earlier than when it actually arrived) but it Ardour can't send it to the speakers in that fasion. That would mean playing it before it arrives, and Paul is so lazy he can't even be bothered implementing a working time machine, despite nearly ten years of development.

If you just listen to the tracks you've recorded there should be no delay between them (and the click for that matter), right?

rufustfirefly
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I wouldn't go so far as to say Paul is lazy. He works his ass off making a free-as-in-speech professional audio suite -- you should at least appreciate that.

If you want a "time machine", try jack's time machine, which has been around for a while.

There are many, many issues which may effect latency. Are you running a realtime kernel and/or distribution? If not, try something like ubuntustudio, which has that stuff baked into it.

Also, you might want to consider investing in some sort of external A/D converter, since you're going to pick up computer clock chip noise with an internal sound card. USB devices aren't the best with latency, but if you want cheap you can try something like the Behringer UCA-202, which works fine for limited channel recording. You might want a nicer card which supports full hardware monitoring, but it might be a bit pricey.

If you're doing single channel recording, you might be better off with something simple like audacity, since you're not actually using any of the crazier features ardour has to offer from what I'm reading.

peder
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Believe you me; if Paul had implemented a time machine that, in this case, is able to play back sound before it's even recorded he'd be getting a Nobel prize. I was just making an ironic joke.
BTW, Steve Harris' time machine just works backwards in time as it keeps a recording of the last 10 or so seconds for you to save. This would have to be forward in time.

From what I understand jcsa's problem isn't really a problem; he can (for some strange reason) use a very low latency on his Intel card. It's just that when he chooses to increase the latency he gets delays, which are probably due to him using Ardour as the "monitor" for his input.

Oh, and the magic jack latency formulae is "periods per buffer" * "frames per period" * 1000 / "sample frequency". And this is apparently the round trip latency since Ardour in your case only displays half, i.e. from input to disk.

allank
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Yeah .. I'm pretty impressed with that latency you are getting too. I had to buy a decent M-Audio card before getting anything like that (btw you may benefit from such a card .. even a 2nd hand delta 44.. as you can do hardware monitoring)...

You can still do h/w monitoring on your current setup but only the input track.. this is simple use the monitor or headphone output from the mixer.. not from ardour. I don't know how useful this is for you though.

BTW ... where is that time machine... (not the LADSPA one)..

vandy (not verified)

Probably I am lucky What I understand jcsa’s problem isn’t really a problem; he can (for some strange reason) use a very low latency on his Intel card. It’s just that when he chooses to increase the latency he gets delays, which are probably due to him using ArdourAlfa