Latency on USB input from PODxt

[memphiskat]

I've recently started using the Beta 1.3 on my iMac running OS 10.4.11

I just connected my Line 6 PODxt via USB for the first time (using 1.3) and simply want to monitor my guitar
playing. I get unacceptable latency when directly monitoring my playing through Audacity. I tried setting the
audio buffer to 0 under Preferences:Audio I/O and still get unacceptable latency. I never got this when using Audacity 1.2.6.
I downloaded 1.2.6 again to check and yep, no latency. I don't want to monitor though my POD because I use my computer
speakers to monitor and would have to use headphones to monitor through the POD.

I did some searching hear and don't see an answer. I have read about and understand the audio buffer and latency correction
settings. This is a latency directly on the input monitoring, and not on playback and recording like when recording to multiple
tracks. I get that there's always going to be some latency, but whatever latency is present when using 1.2.6 it is unnoticeable.
The latency in 1.3 makes using it for monitoring my playing impossible.

Any ideas?

Karl

[steve]

I'm guessing that you have got "Software Playthrough" selected in v.1.3.4 ("Edit->Preferences->Audio I/O") which is sure to cause noticeable latency. No idea how you've got 1.2.6 set up to avoid it, but I'd have a look there first and simply copy the settings to 1.3.4

[memphiskat]

Yes, I have "software playthrough" selected in 1.3.4 I use my computer speakers for monitoring
so....... if you deselect that it will eliminate the latency,.... but also my ability to monitor the signal

I actually have the preferences pulled up on both versions simultaneously to compare settings. In the audio I/O
pane they are basically the same. Only differences are in the Playthrough check lists, 1.2.6 has an additional option...
"_ Do not modify audio device settings (such as sample rate)" This is checked in 1.2.6
Additionally, there are no settings for Latency in 1.2.6 like the AUdio to buffer:, and Latency correction:

Can't figure it out. I don't have latency like this in any of my other software programs (Garageband, ect.) I use with my POD (always
connected through USB) I like the 1.3 version for editing two track and other previously recorded audio, but this latency
with my POD makes this version unusable as a multitrack recording program.

Karl

[steve]

Yes, I have "software playthrough" selected in 1.3.4 I use my computer speakers for monitoring

So how do you have it set up in 1.2.6 - how are you able to monitor the recording with that?

[memphiskat]

My setting are almost identical. I pasted screen shots below. Never did this before, hope I did it right.
The first one is the Audio I/O tab of 1.3.4 and the second is the Audio I/O tab of 1.2.6
They are vertually the same. The only difference is the audio in buffer and latency correction
setting in 1.3 that are not available on 1.2.6 and the "Do not modify audio device...." check box on
1.2.6 that is not an option on 1.3.4 The Quality Tab settings are identical between 1.2.6 and 1.3.4
Again this is latency I'm experiencing on the input signal. I play a note on my guitar plugged into my PODxt and
that plugged into the iMac via USB and the note is delayed coming out of my computer speakers. Yes, I am using
software playthrough on both programs, but I get no or near no latency in 1.2.6 and unuseable latency with
1.3.4. I know I could monitor through headphones plugged into my POD, but I don't want to. My POD actually sits
entirely inside a drawer in the desk the computer's on and I use my iMac speakers to monitor. I just can't figure out
why I don't get this delay in 1.2.6, but I do in 1.3.4 After doing some searching here and at the Nable Audacity Forum
I get the feeling it may be with Portaudio v19, but those threads go beyond my technical knowledge in a hurry

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[steve]

Hi again
When posting screen shots, jpeg or gif formats are better (more browser compatible) than tiff.
No problem though, I just downloaded the images to view them

I'm assuming that the playback device in each case is the same, although the terminology is slightly different.

I see that in both cases you have both "Hardware Playthrough" AND "Software Playthrough" selected.
(I don't have a Mac so I'm not able to test this, but I'll try and suggest some ideas and hopefully you'll be able to resolve this)

If you have no (very little) latency in 1.2.6, then it must be using hardware playthrough - try testing this by de-selecting "software playthrough", leave "hardware playthrough" selected, and see if you are still able to monitor the recording.

The "Audio Buffers" is to prevent the sound from breaking up if your computer is unable to stream the audio data through your sound card fast enough - If you are not getting any glitching (interrupted playback), then your hardware is probably handling this itself.

The "latency correction" item in v.1.3.4 is to adjust the position of a recorded track, to compensate for any recording latency. There is an article elsewhere on the forum about setting that up correctly, but this is not your main problem, so for now just set it to 40 milliseconds and we can come back to that later if necessary. Latency correction in v.1.2.6 is not adjustable, it's just set for a default value which should be "close enough" for most.

"Do not modify audio device settings" (Audacity 1.2.6)
Audio hardware will often have a default, native, sample rate and bit depth, for example with SoundBlaster Live cards there is a native sample rate of 48000 Hz. For hardware playthrough to be possible, the data may need to be in the default format that the audio device requires. In Audacity 1.2.6 this is easily achieved with this check box. In Audacity 1.3.4 you may need to manually set the sample rate and bit depth for the project (Edit->Preferences->Quality).

Since you have noticeable latency in 1.3.4, I'd guess that it is using software playthrough (even though you also have "software playthrough" selected as well). This could just be a difference between which option Audacity defaults to when both options are selected.

Assuming that monitoring was fine in 1.2.6 with "software playthrough" switched off, try doing the same for 1.3.4
If you find that in 1.3.4 there is no sound coming out (but there is in 1.2.6), then try changing the "quality" settings for the project. If you don't know what the default settings should be, try combinations of 44100 Hz, 48000 Hz, 16 bit, 24 bit, 32 bit (these are the most common).

If this doesn't work, then I'm out of ideas and unless someone familiar with Macs can suggest anything else, you may need to resort to monitoring directly from the Pod.

[memphiskat]

Ok, JPEG or GIF, got it

I tried the following...

Audacity 1.2.6
software checked, hardware checked - ouput, no latency
software unchecked, hardware checked - no output
software checked, hardware unchecked - output, no latency
do not change hardware setting of device...unchecked and checked - output, no latency

Audacity 1.3.4
software checked, hardware checked - output, latency
software unchecked, hardware checked - no output
software checked, hardware unchecked - output, latency

all of these outcomes are to be expected, minus the latency

I also tried all the possible combinations on the quality tab, with respect to
sampling frequency, bit depth, ect. with no change

So.... I can only conclude that something that has changed between the stable version
1.2 and the Beta is causing the latency.

Is anyone using 1.3.4 with a Mac and a USB device and not getting latency when monitoring
through the software?

Karl

[steve]

Rats.

So.... I can only conclude that something that has changed between the stable version 1.2 and the Beta is causing the latency.

Not quite. Software playthrough will always cause noticeable latency, it can be minimised, but can't be avoided. Audio drivers for external devices (USB / Firewire) frequently have strange implementations that cause recording and playback settings to not work as expected. A typical problem is that there is no way to control the input level. It seems that your problem is yet another driver quirk. To get zero latency, your setup must be using hardware playthrough in 1.2.6 (irrespective of the settings in Audacity).

Work is currently going ahead on Audacity 1.3.5 and 1.4, so hopefully this issue will be fixed in the new version when it comes out. Unfortunately it seems that you will have to use 1.2.6 for recording. You can still save your 1.2.6 project after you have finished recording and then open the project in 1.3.4 for further editing and processing, but note that once you have opened it in 1.3.4 you will not then be able to reopen it in 1.2.6.

[memphiskat]

Thanks for trying to help with this. I've been using 1.2.6 for monitoring and recording and using 1.3.4 for
the final editing like you suggested.

One thing I'm not quite clear on. If I'm using hardware monitoring I would have to have my headphones or speakers
running from the outputs on my USB device (in this case my PODxt) right? Is that is what they are refering to as hardware
passthrough? In 1.2.6 I am using my speakers connected directly to my Mac, that would have to be a software playthrough
configuration correct? Or am I missunderstanding and it's possible that the signal is going directly from the USB output of my
PODxt through my computer to the internal speaker outputs on the back of my Mac and "bypassing" the software?

karl