Dynamic Rumble Filter

[steve]

I've come round to your idea jtp_60
My latest code uses an envelope follower to control the cut-off frequency of a high pass filter. The envelope follower uses RMS values takes over 100 samples, which stops the filter from jittering on crackles. Including a fixed sub-sonic filter takes care of any DC or very low frequencies while having negligible effect on the real audio, while a gentle slope (6dB /octave) rolls off the bass when the audio level drops below the threshold level.
It seems to work pretty well, but what we really need is some audio samples for testing.
I'll post the code as soon as I've made it into a plug-in.

[davidcw]

I've come round to your idea jtp_60
My latest code uses an envelope follower to control the cut-off frequency of a high pass filter. The envelope follower uses RMS values takes over 100 samples, which stops the filter from jittering on crackles. Including a fixed sub-sonic filter takes care of any DC or very low frequencies while having negligible effect on the real audio, while a gentle slope (6dB /octave) rolls off the bass when the audio level drops below the threshold level.
It seems to work pretty well, but what we really need is some audio samples for testing.
I'll post the code as soon as I've made it into a plug-in.

Hi Steve,
Did you find coding your filter was possible to do?
Here is a sample from a turntable with pops and
crackles reduced, but the turntable rumble and idler
noise is plainly audible.
http://rapidshare.com/files/281649176/Rumble_test.wav

[steve]

Oh brilliant - I'd forgotten about this.
Thanks for the audio sample - this should be a really good one for testing as it has some nice deep bass with those double basses at the beginning.

As it is, it works as a "proof of concept" but it sounds terrible. It is really obvious where the effect cuts in and out. It needs a some major tweaking, and that audio sample will be a great help.

[davidcw]

Here is a sample of groove noise after the pops and crackle have been reduced.( I used Wave Corrector)
I was thinking it might be easier to just use Dominic Mazzoni's Noise Removal, and take a noise profile
from the groove noise? ( Perhaps after also applying a LP filter to the groove noise sample.)

http://rapidshare.com/files/281934431/Groove_Noise.wav

[jtp_60]

You propably need to improve the grounding from turntable/pre-amp to PC/audio interface (try different places for ground on PC side (I normally ground through sound card ground but that does not always work that way)) or/and fix the PSU from turntable/pre-amp (try by either improving the PSU or by just removing it out from the device). That background noise there is, may come also from external source as well (power line, charger, PC monitor, etc. there are many other possible sources). Keep turntable/pre-amp far from those.

Untill Steve gets everything working, you can use this (it's a VST implementation of std. static 12th order HP filter @ 60Hz). If you like to tweak the filter more, just download the SynthEdit package + Butterworth/Chebyshev filter packages from Christian-W Budde's site. Why @ 60Hz ... if you just plot the spectrum for groove_noise.wav.


Juha

[steve]

Audacity already has a high pass filter, so there's really no need to install a VST effect.