Audiobox USB = Digital Noise on Capture Port

[mikey38654]

Hi Guys and gals,

I have recently began using Ubuntu Studio (and, in fact, Linux altogether, so Newbie on both ends), and I have worked my way into figuring out the basics of JACK. However, I am exhausted of figuring things out and manipulating my way in circles with Linux and am hoping for some easy help.

I acquired a like-new M-Audio AudioBox USB a few days ago and have been trying to get it to work. I have found that if I boot Studio with it plugged in, JACK places it as the System audio card. That's fine. I am listening to a CD with Audacious and it's beautiful sounding. However:

My capture_1 and capture_2 ports are Noisy! They are producing this digital noise that only comes through when capture_1 and capture_2 are connected (with JACK) to anything leading to the output. Straight to output or through apps (sounds prettier through the effects processors but that doesn't help). For example, in JACK, system:capture_1 --> system:playback_1 makes this noise, as well as capture_2 --> playback_2.

Problem persists wih nothing plugged in to the inputs on the AudioBox. Voice does come through alongside noise when using mic, but it is distorted. Phantom Power is not activated.

What is up with this? My input sounds like the Sputnik satellite! More realistic comparison - it sounds like a bad cable between a guitar and amp.

I just had a thought: while the inputs come up as stereo in JACK (hence capture_1 and capture_2), JACK is only seeing one stereo input, not two mono ones, and this AudioBox has two mic/instrument inputs on it (mono I suppose). I wonder if this is causing the problem? I haven't had latency issues I don't think, but if there's anything I can check please let me know.

Thanks guys.

[mikey38654]

Oh and this AudioBox has a headphone monitoring feature that doesn't go through the computer (basically, mic --> headphone direct) and the audio is clean on that end, too. It seems as though the problem is in the cable or in the conversion.

I'm going to check my sample rate. I think it is set to 48K, which matches what the AudioBox Box says it works at.

[mikey38654]

Well, I just learned something.

JACK is, in fact, seeing two mono inputs, capture_1 is left input and capture_2 is right input. Each input is producing the digital noise I'm experiencing, not just one.

[mikey38654]

noisyaudiowithvoice.png (39.55 KiB) Viewed 303 times

May I present, this picture. It is what was recorded in Ardour as I spoke into my microphone with the digital noise present. Notice also the VU meter... when I mute the Audio1 channel, the noise remains and the VU meter remains lit up. If I mute the Bus it's assigned to or the Mains, the noise goes away from my headphones, but the Audio1 VU meter is still lit all up (however I see how this makes sense since at this point Audio1 is not muted).

For clarity, I do realize that when I took the screen grab, the "maybemidi" channel was muted and not Audio1. This was a different time from when I tested muting the Audio1 channel.