Loud hum when playing back soundfile + other noisiness issues

#1

Testing play fn for simple WAV playback. While the file is playing there is a terrible buzz that sounds something like a distorted sawtooth. The buzz is as loud as the sound material in the file, and it stops as soon as the sound is finished playing.

I was hoping (for an installation) to be able to combine playback of WAVs with audio thru from electret condenser mics, blending realtime soundscape with other binaurally treated sounds.

I have two electrets connected and working (having obtained a couple of the SparkFun ones) but they are also quite noisy. Not self-noise hiss -- the mics are certainly noisy -- but a continuous quiet buzz, mostly in the left channel.

I fear unless I can eliminate the noise problems that the Axoloti won't be useful for this project. Any help is welcome!

#2

sounds odd... and certainly not an issue ive faced with playback

you need to narrow down the problem slightly.

play a simple sine osc to output - check this is not
if this is distorted, look at your gain levels on output etc.

if not, then we know its not axo hardware related, since the audio output path is ok
so you need to check the wav file, ensure it is a 48k raw 16 bit mono file.
(various threads on the forum about preparing raw files for playback with audacity etc.)

use a scope on the output of table play, check to see if its clipping, if not, try to add a gain after, to reduce gain level.

another 'tip' in patch settings, try turning off 'saturation', which increase gain on patch, if your patch has high gain levels/combines a few audio sources, this can be problematic

to get further, you probably need to post your patch and wav file.
also it'd be useful to see a screenshot of the scope connected to the play, so we can see if its clipping.

I cant say anything about the mics, except there is an audio in config object which you should look at to adjust gain etc.... again, I use axo as an fx with audio in, without any buzzing etc.

#3

Thanks for the reply. I'll check the things you suggest.

The audiofile I'm using is definitely 48/16.

Here's my little test patch and the audiofile (dropbox links)

The test patch has basic audio thru from the microphones, plus addition of a highpass filtered version to boost high end as the mics are lacking above 10K.

Here is a recording of the axoloti output demonstrating the problems.

#4

OK... so the bad hum when playing back the audiofile is happening as part of the mic thru signal. The audiofile playback on its own is clean. So I need to track down why the playback interferes with the mic signals.

I'll have to try with some dynamic mics attached to the main input jack as well.

(BTW there is definitely no clipping going on and a sine tone sounds fine.)

#5

Yeah that's pretty bad
Perhaps try taking a line signal in from another instrument, see how that sounds.

#6

also look at the audio/inconfig mic object
this says its for configuring electret mics

#7

Thanks for the suggestion but I think that the inconfig mic object has to do more with bias voltage, which I don't need to worry about since the SparkFun electrets I am using handle that on their own little circuit boards.

I tried rewiring the electrets with better shielded cable and that didn't help a great deal. Disconnected them and tried a pair of dynamic mics connected to the TRS jack, and that works much better. Much less of the hum and no interference when I run the audio file. The general background noise level from the mics themselves is quite high.