Crackling audio? Try CoreAudio Aggregate Devices.

[qo]

I've posted a possible solution to crackling audio in response to a couple threads, but have become convinced (after over a week of use) that this completely solves issues with crackling audio in DP; at least with Apogee X-Firewire.

When selecting Apogee's physical devices within DP (one for AD-16X and one for DA-16X), there are no combinations of Host Buffer Multiplier, Buffer Size, Disk Read/Write Size, etc, that work. All settings I have tried result in crackling eventually. And, I've tried pretty much every concievable combination.

However, if a CoreAudio Aggregate Device is created in Audio/MIDI Setup, and this is selected in DP, crackling audio is history. 100% gone. Vamoosh. Demons cast out! I have no idea why this would be the case other than it must be changing how DP interacts with CoreAudio. But, it does work. (DP 4.6, 10.4.2, G5 dual 2.7).

Maybe this won't be as helpful for those using MOTU's drivers, but I wouldn't rule it out. If you have crackling audio, give it a shot. If this helps, please post here since I'm really curious whether others experience the same results.

[David Polich]

Even though I don't have a ny crackling audio issues, thanks for the VERY helpful information. Nice detective work - much appreciated.

[qo]

Thanks Dave!

[melodesiac420]

Originally posted by qo:

However, if a CoreAudio Aggregate Device is created in Audio/MIDI Setup, and this is selected in DP, crackling audio is history. 100% gone. Vamoosh. Demons cast out! I have no idea why this would be the case other than it must be changing how DP interacts with CoreAudio. But, it does work. (DP 4.6, 10.4.2, G5 dual 2.7).

Maybe this won't be as helpful for those using MOTU's drivers, but I wouldn't rule it out. If you have crackling audio, give it a shot. If this helps, please post here since I'm really curious whether others experience the same results.

I use a M-Audio Firewire Solo and I'm experiencing the same crackling audio probs. (I've tried changing everything, host buffer multiplier, buffer size, work priority all to no avail!

I know I may seem like a complete DP noobie, but
how would I go about creating a new audio device in audio/MIDI setup?

[qo]

You need to open /Applications/Utilities/Audio MIDI Setup

Once there:

1. Click the Audio Devices tab
2. Mouse over to Audio->Open Aggregate Device Editor (in the menu bar) and open the device editor
3. In the editor, click the "+" button
4. Your M-Audio should appear in the list below. Click the "Use" button in its row
5. Double-click the default name of the aggregate device in the top pane and rename it to what you want to call this device
6. Click the "Done" button
7. Quit

Now, in DP, select the device you just created in Audio/MIDI Setup in the same way you would select any hardware device.

<small>[ August 03, 2005, 07:45 AM: Message edited by: qo ]</small>

[grimepoch]

Interesting, I am gonna have to try this. By crackling you mean that you get pops and clicks once in awhile? I noticed I was getting this when I started using the internal audio port (TOSLINK) with my 896. At first I thought it was a timing issue, but that just makes no sense to me. I increased the buffer size from 128 to 256 and it happens less, but I swear I still hear it once in awhile.

Will try this tonight with 128 buffer setting and see if the problem goes away, will post here so you know for others.

And thanks, I was just about to write about this.

[qo]

Originally posted by enc0der:
Interesting, I am gonna have to try this. By crackling you mean that you get pops and clicks once in awhile?

Hi enc0der. In my setup, I was getting a raspy digital distortion intermittently, especially with certain sustained sounds like e.g. organ. It's sort of like you'd hear if you were overdriving an AD's inputs i.e. harsher than overdriven analog stuff. I could temporarily fix things by changing ANYTHING in DP's Hardware Setup. The fix would last a minute or two, and then the problem would return. But, the Aggregate Device fix has proven itself over a couple weeks now.

Clicks/pops still rear their heads in my setup, but I understand these since they correspond with DP's CPU Performance meter maxing out. To solve this, the standard sorts of things apply (increase buffer size, freeze tracks, etc).

I wouldn't rule out that this "crackling" issue is specific to Apogee (or maybe to driverless CoreAudio devices, like Apogee), but would love confirmation from you, or others, if this hack helps.

Thanks!

qo

[grimepoch]

I believe mine was the same as yours, trying to use two devices inside of DP using DPs multi interface selection ability. As you, I observed that the cracking would only occur with sounds playing, and your description is about the same as what I'd say.

Just as you, I could get it to go away for a little bit, but it would come back. I couldn't figure out what it was until today.

Just as you, if I create an aggregate device and use the built-in audio with the 896 at the same time, the crackling is gone. However, by trying to adjust the buffer size or sampling rate, DP crashes quite repeatily on my system. So the plus is that the crackling is gone, the minus is that stability for me just left through the window.

So, beyond that I did a test, to see the CPU usage with aggregate mode and then using the DP method. CPU usage was the same. Note that I have nothing even using the built-in audio at the moment, meaning the input and the output are not being used in the current project.

So, I went into the setup and removed the internal interface from the list, and didn't have to change anything in my project because I wasn't using it. Reran the song that was peaking the CPU, not it's using 50% less CPU. Interesting. I am not exactly sure why that is, but I get a huge performace hit trying to use it. (Which means, I am just not gonna use it right now).

I'd be curious to know in your situation, if you have a project using only one interface, if you remove the other one, do you get a performance increase, or maybe this might just have to do with the internal audio.

Regardless, for now I think I'll just go back to analog on my Mini and feed it into my mixing board that goes to one set of inputs on the 896.

[qo]

Interesting results Rick. I did actually have some instability initially after creating and selecting the Aggregate Device. The first time I selected it, DP crashed. So, I rebooted and tried again and things worked, but were unstable in terms of spinning beachballs and crashes. So, I deleted prefs and started from scratch. I also went into Audio Bundles and deleted all bundles and started from scratch, giving the Aggregate Device a short meaningful name. Ever since, things have been running very smoothly.

But, I don't have internal audio selected within DP's Hardware Setup. Maybe that does have something to do with it.

[melodesiac420]

Originally posted by qo:

2. Mouse over to Audio->Open Aggregate Device Editor (in the menu bar) and open the device editor

In my audio/MIDI setup screen, under audio devices, I do not have an "Audio" option in the menu bar. I just have: Audio MIDI Setup : MIDI Devices : Window : Help

None of the drop down's have an option of Open Aggregate Device Editor.

I have audio/MIDI setup v2.0. Is this a dated version?

[Shooshie]

qo, I think you're on to something here. This could be big. Maybe if we go to them with the solution, we can convince Apple/MOTU/Apogee/whomever that all is not well in the Land of Core Audio.

qo, let me ask you if your problem is similar to mine:

1) no pops on playback.
2) pops when I play my keyboard through DP
3) the pops themselves seem to follow a cycle, as if they are some kind of filter coupled to the complexity of what I'm playing. When holding a note or playing a passage, the first pop begins about when I start playing, then the second is about 20% quieter, the 3rd 20% quieter still, as well as about 50% later. The fourth is much quieter, and about 50% later than the previous one.

In other words, it's as though they are on a spiral wheel, getting quieter and further spaced apart with each pop. Then it repeats when I play the next note or passage. The pop cycles can overlap, making them sound more complex, but closer analysis shows that it's just multiple occurrences of the same cycles, some louder than the others--connected to velocity, perhaps.

4) they do not seem to record in the track. The tracks are good and play back fine.

As that somewhat like what you're getting?

Shooshie

[Shooshie]

Some more questions:

Do you have any idea what Aggregate Device means? For now, I'm assuming that it means that it's creating a virtual interface in which you can combine any number of inputs/outputs from "real" devices. Example: I could create an aggregate device consisting of a 1296 and a 2408 and call it "The 24-12", and all the inputs from those two devices would show up within one virtual device.

I could create another aggregate with 896 and Soundsticks. These, then, become my devices as seen by DP and other audio software.

But why? Why would Apple make this a possibility? And why would it stop the crackles?

Next question: Should we de-select the "real" devices and ONLY use the Aggregate Device? If we still select the real device, will we still get pops? Or is just having the aggregate device created enough to stop the pops? I guess that one is pretty obvious, but I'm curious nonetheless. I'll try to answer it myself.

This is very interesting. Until today, I never knew that option existed. Now, it may be the answer to all my problems. Too soon to tell. I'll report back when I know more. Until then, please do share what you learn.

And thanks a million to qo. I swear, that young man is a genius. When I have those questions that cause most musicians to turn pale and walk away--like UNIX, System, and the deep-level stuff--I go to the psychedelic onion. Or make that Quality Onion! QO!

Shooshie

[Shooshie]

Hello? Anyone here? Sorry to be monopolizing the posts in this thread. It's very interesting to me.

qo! It's working! I have:

••• 896
••• 1296
••• 2408 mkII
••• And occasionally I'll route things out through the Soundsticks for one reason or another, so it's in the list, too.

I made an aggregate device, but when I played soundbites there was the old pop. (Now I'm thinking it's connected to tempo analysis, because it seems to happen where the beats are... maybe a coincidence) So, I deselected all the "real" devices from the hardware menu and went only with the Aggregate Device. Played soundbites and pops are gone. TOTALLY.

But only after deselecting the other devices. It didn't matter if I was playing through the Aggregate Device if the other devices were still selected in the list. Only when I deselected them did the pops go away.

Shooshie

[iMAS]

I wonder what Motu would have to say about this.

[qo]

Hi melodesiac420,

Not sure what to make of the absence of the menu. Do you have any audio devices installed? Perhaps AMS doesn't see any devices and so doesn't display the menu?

Hi Shooshie,

Yes, the cyclic/periodic behavior you describe sounds similar. It's almost as if a buffer is being overrun, corrupting the stream, which causes the distortion. This is what I've been thinking actually. Some buffer is getting throttled (backed up) and is dropping samples. It then recovers for a bit and gets backed up again, etc. And, yes again, it only happens when playing through a keyboard (either a VI, or an external synth). So, perhaps it's an interaction with MIDI (e.g. MIDI interrupt occurs, diverting CPU away from CoreAudio, causing buffer to get backed up).

Aggregate Device (AD) is exactly what you describe. It's a virtual device composed of multiple physical interfaces. In DP, you'd select ONLY the AD.

But why? Why would Apple make this a possibility? And why would it stop the crackles?

I believe they did it so that individual apps wouldn't have to do what DP has been able to do for ages. Specifically, rather than incorporate this into Logic, they made it a system service that all apps can take advantage of.

As to why it stops crackles, my GUESS is that it's adding a buffer somewhere. It could be that, in order to aggregate multiple devices, CoreAudio has to compensate for each device's inherent latency in order to present a single latency to the applications that use the Aggregate Device. For example, say you use a M-Audio and an Apogee and these have different inherent latencies. Now suppose you're recording stereo using port 1 of the M-Audio and port 1 of the Apogee (maybe these are ports 1 and 9 of the Aggregate Device). The application has to receive these streams in sync or you'd get phase shift. Anyway, that's the only reason I can think of.

When I have those questions that cause most musicians to turn pale and walk away--like UNIX, System, and the deep-level stuff--I go to the psychedelic onion. Or make that Quality Onion! QO!

Aw, shucks. Thanks!

<small>[ August 03, 2005, 09:11 PM: Message edited by: qo ]</small>