Noise Reduction filter in foobar

2009-03-09 23:08:13

does someone knows of a noise reduction dsp filter, or how can it be accomplished with known dsp filters (not vst)?
thanks

Noise Reduction filter in foobar

Reply #1 – 2009-03-09 23:28:16

well I looked on the 3rd party component site
http://fb2k.org/section.php?section=4

maybe the first one, looks promising
but I didn't read them all

look for yourself

take care
Chris-

Noise Reduction filter in foobar

Reply #2 – 2009-03-09 23:38:38

well, it's noise enhancer and it doesn't reduce it, right - i'm looking for opposite

Noise Reduction filter in foobar

Reply #3 – 2009-03-10 00:35:28

okay  but there a more on the site

Noise Reduction filter in foobar

Reply #4 – 2009-03-10 00:35:47

I don't think there are any, but I'd love to see someone have a crack at emulating the HUSH SSM2000 noise reduction IC in software as a plug-in for Foobar2000, or at least as closely as can be done without the risk of being sued.

The datasheet can be downloaded freely in PDF format HERE.

The underlying principles are very simple in practice although I have no idea how this translates in terms of complexity at the software level. It's basically a voltage-controlled lowpass filter (VCF) with a slope of 6dB per octave and a cut-off frequency determined by the measured HF content of the incoming signal followed by a voltage-controlled amplifier (VCA) set up as a dynamic expander with an expansion rate inversely proportional to incoming signal level. See figure 20 on page 8 of the datasheet linked to above for a graphical representation of the dynamic expander's transfer function. The incoming signal for the control voltages applied to the VCF and VCA is also preconditioned via highpass filters as shown in figure 22 on page 9.

A full level, full spectrum music input signal leads to an output bandwidth of around 20kHz with almost no dynamic range expansion, and an input consisting of nothing but white/pink noise at around -70dB leads to an output bandwidth of around 1kHz and a 16dB downward expansion. The combined effect of both methods drops a -70dB noise component down to around -95dB. The attack and decay times of both the lowpass filter and the dynamic expander are carefully chosen to make the effect as transparent as is feasibly possible and are shown in graphical form in figures 26a and 26b repsectively on page 10 of the datasheet linked to above. There is also a level detector involved to measure the mean level of the background noise, so no level calibration is required by the end-user.

I built said beasty into a high quality cassette deck several years ago, partly as a means of reducing tape hiss when transferring tapes to the PC, and it works amazingly well. In its standard guise with 25dB of overall noise reduction, the circuit is claimed to be suitable for decoding Dolby B encoded sources, although I did modify the circuit slightly to give a variable NR range of 6dB to 25dB to suit different source material including the handling of non-Dolby B encoded sources. Whether or not the resultant NR could be considered transparent would obviously come down to the end-user in question and the aggressiveness of NR used, but I always found the resultant output to be preferable to the original input in terms of perceived quality, certainly at the less aggressive end of my 6dB to 25dB adjustment range.

Will someone please have a crack at this as a plug-in for Foobar2000. I'm more than happy to be a testing guinea pig if you want a DSP compared to the silicon original.

Cheers, Slipstreem. 

Noise Reduction filter in foobar

Reply #5 – 2009-03-10 01:28:02

thanks for the extensive response
native dsp filter would be great of course
i tried with xover + channel mixer but just can't get it to work
no matter how carefully you are about your music library, there are always some tracks (rare records, live material, circumstances  etc) with all kinds of noise in them, in which case i use vst, but for this install i need dsp (without vst) solution if there is any