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I'm looking for an algorithm for hiss reduction of speech (and/or other
aural) signals.

Any ideas?

Thanks,

John

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John Cristion wrote:
> I'm looking for an algorithm for hiss reduction of speech (and/or other
> aural) signals.
> 
> Any ideas?

Couple of things come to mind:

1) use a low-pass filter with variable cutoff frequency,
and adjust the frequency as a function of the amount of
high frequencies present in the signal (the input signal).

2) FFT -- eliminate the values that are below a certain
threshold.  You could make that threshold adjustable, or
try tricks like detecting when the signal is absent and
you just have background noise/hiss -- the mean value
of the spectrum at that time can be used to set the
threshold.

HTH,

Carlos
--

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Carlos Moreno <m...@xx.xxx> wrote in message news:<
> 2) FFT -- eliminate the values that are below a certain
> threshold.  

I believe you wanted to say "above a certain threshold", right?

--Frank

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Frank wrote:
> Carlos Moreno <m...@xx.xxx> wrote in message news:<
> 
>>2) FFT -- eliminate the values that are below a certain
>>threshold.  
> 
> 
> I believe you wanted to say "above a certain threshold", right?

No, *below* a certain threshold...  Or do you want to eliminate
the speech and leave only the background hiss?

Don't know if the phrasing I used suggests something else, but
the idea was:  take the FFT;  loop through the N values and
replace those that are below a threshold with 0;  then take
inverse FFT  (with proper overlap methods).

Carlos
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Frank wrote:

> Carlos Moreno <m...@xx.xxx> wrote in message news:<
> 
>>2) FFT -- eliminate the values that are below a certain
>>threshold.  
> 
> 
> I believe you wanted to say "above a certain threshold", right?
> 
> --Frank

No. Hiss has (we hope) low amplitude, and small components have small
importance. By eliminating components too weak to matter much, the
quality of signal might be improved.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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"John Cristion" <J...@jhuapl.edu> wrote in message
news:<c5k7at$aip$1...@aplcore.jhuapl.edu>...
> I'm looking for an algorithm for hiss reduction of speech (and/or other
> aural) signals.
> 
> Any ideas?
> 
> Thanks,
> 
> John

John,

If you look over the right interval, the speech will be changing
characteristics while the hiss will not.  In other words, the hiss is
stationary, the speech is not.  Exploit that.


Maurice Givens

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John Cristion wrote:

> I'm looking for an algorithm for hiss reduction of speech (and/or other
> aural) signals.
> 
> Any ideas?
> 
> Thanks,
> 
> John
> 
> 

I have seen an adaptive filter design in the amateur radio literature (I 
think it was "QST", but it may be "QEX") that capitalizes on the fact 
that speech is fairly highly correlated while hiss is not.  The 
adaptation is set to be fairly fast, and the filter passes the 
correlated part.  This would have been about 10 years ago or so -- if 
you find it you may find the source material that they were working from.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Carlos Moreno <m...@xx.xxx> wrote in message
news:<Xvwfc.24947$V...@weber.videotron.net>...
> Frank wrote:
> > Carlos Moreno <m...@xx.xxx> wrote in message news:<
> > 
> >>2) FFT -- eliminate the values that are below a certain
> >>threshold.  
> > 
> > 
> > I believe you wanted to say "above a certain threshold", right?
> 
> No, *below* a certain threshold...  Or do you want to eliminate
> the speech and leave only the background hiss?

No I was thinking of cutting off the values at a certain threshold...
like a peak limiter does, to suppress excessive peaks in the HF area.

Now I see what you meant.

--Frank

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"Carlos Moreno" <m...@xx.xxx> wrote in message
news:KIifc.19024$u...@weber.videotron.net...
> John Cristion wrote:
> > I'm looking for an algorithm for hiss reduction of speech (and/or other
> > aural) signals.
> >
> > Any ideas?
>
> Couple of things come to mind:
>
> 1) use a low-pass filter with variable cutoff frequency,
> and adjust the frequency as a function of the amount of
> high frequencies present in the signal (the input signal).

This is a fairly simple algorithm to implement.  For an example of a commercial
product that does this, see http://www.behringer.com/SNR2000/index.cfm?lang=ENG.
From reading the manual, you may be able to get a pretty good idea of how it
works.

As has been mentioned by others in this thread, more complex algorithms relying
on statistical properties also exist.  CoolEdit has implemented this and last I
knew had a free demo available for evaluation.

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Frank wrote:

> Carlos Moreno <m...@xx.xxx> wrote in message
news:<Xvwfc.24947$V...@weber.videotron.net>...
> 
>>Frank wrote:
>>
>>>Carlos Moreno <m...@xx.xxx> wrote in message news:<
>>>
>>>>2) FFT -- eliminate the values that are below a certain
>>>>threshold.  
>>>
>>>
>>>I believe you wanted to say "above a certain threshold", right?
>>
>>No, *below* a certain threshold...  Or do you want to eliminate
>>the speech and leave only the background hiss?
> 
> 
> No I was thinking of cutting off the values at a certain threshold...
> like a peak limiter does, to suppress excessive peaks in the HF area.
> 
> Now I see what you meant.
> 
> --Frank

It's easier to describe in analog. It's called center clipping in time, 
and this is the equivalent in frequency, like H.H.Scott's Dynamic Noise 
Suppresser.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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