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Noise Issue Problem with Filtering

June 29, 2011 | 4:03 am
– Pasted Max Patch, click to expand. –

In my patch above, I am experiencing some high frequency noise (I am hearing what sounds like narrow band ringing somewhere in the 1 to 8 KHz range) that is not wanted and very unpleasant.

Basically, I am using the filtering approach to make a low frequency patch/synth. I am in the early stages of the process, and though I am not new to MAX/MSP, I am a noob when it comes to filtering and subtractive synthesis. So I suspect I maybe doing something fundamentally or amateurishly wrong.

Of other note, if you listen to the sounds produced, the ringing noise seems to be in the same band no matter what I use as the generating signal (tri~, triangle~, square~(a very simple patch I made), or noise~), which leads me to believe its not aliasing, since it doesn’t appear to move when I change the frequency or filtering center frequency. I normally initiate the patch as such:

fc: 40 to 80 Hz
df/dt & A: 0
Filter Type: bandpass
Harmonic Cutoff: 1
(also I use unity gain, have tried Q > 1 and sometimes very high to try to get rid of the hi freq, but again that hasn’t been working)

Finally, the only ‘success’ I have had is with masking the sound by using higher value of fc, but that again beats the purpose of the exercise. All help/suggestions appreciated.


June 29, 2011 | 6:05 am

I didn’t spend much time with it, but I didn’t hear what you describe. I’m not saying it isn’t there, just that I didn’t hear it with a quick listen.

What are your DSP settings?


June 29, 2011 | 8:55 pm

My DSP settings are what I believe to be normal (44.1 Hz, 16-bit, Stereo).

Listening to it over and over, I realized what it reminded me of: the high pitched alert from most fire alarm systems for commercial buildings (goo.gl/OGmk7); it's an annoying sound that I've become accustomed to at the end of a semester when a panicky student attempts to buffer up some more cram-time. None of these artifacts seem to be present in the screen captures of the spectrogram.

I recorded the sound, various times and have partially concluded that the source of the noise is in the path between the MSP DAC driver and my sound card. Again it could be my crappy sound card, I might be using a bad driver, or I might be doing something wrong with the DSP settings, but I am not experienced enough to which.

"test (MSP).aif" is a sample recording from inside the patch, in which the sound is not present when I play it outside of MSP, but if I put it in a buffer and play it, the I still hear the noise.

"test for noise.wav" is a recording of my Audio output of my pc via multi-track audio recording software (by analog routing of output to input). It is considerably noisy, due mostly to the use of the built-in sound card of my lap top. However, the high pitch noise can be heard, despite the addition of the more generic noise.

I would really like to figure this out. Any suggestions would be gladly appreciated.

(though my problem seems to be system specific, I am including the patch with the exact parameters used to generate the recordings)

– Pasted Max Patch, click to expand. –

[attachment=165395,2404] [attachment=165395,2405]

Attachments:
  1. TestSpectrogram.png

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