Multiband Amplitude Compression in Freq. Domain

Dear all, 

I would like to get started on Multiband Amplitude Compression in 
the Frequency Domain. So basically I would like to do the processing 
like Compression of the signal on frequency spectra (bins). 

Can anybody suggest any links or references from where I could 
get an understanding of how can I do it ? 

Thanks in advance, 
AV. 

"aaab" <52020@dsprelated> wrote in message 
news:E5OdnXuCVY7pYlPNnZ2dnUVZ_o2dnZ2d@giganews.com...
> Dear all,
>
> I would like to get started on Multiband Amplitude Compression in
> the Frequency Domain. So basically I would like to do the processing
> like Compression of the signal on frequency spectra (bins).
>
> Can anybody suggest any links or references from where I could
> get an understanding of how can I do it ?

Dolby A noise reduction system:

http://en.wikipedia.org/wiki/Dolby_noise-reduction_system


Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com

http://www.proaudiodsp.com/

Hi Greg, Vladimir, et. al.,

Thanks for your replies. 

I am seeking much more details in terms of 
the core algorithm and sound pressure measurement to be used. 

Regards,
AV.





>http://www.proaudiodsp.com/
>

>Dear all, 
>
>I would like to get started on Multiband Amplitude Compression in 
>the Frequency Domain. So basically I would like to do the processing 
>like Compression of the signal on frequency spectra (bins). 
>
>Can anybody suggest any links or references from where I could 
>get an understanding of how can I do it ? 
>
>Thanks in advance, 
>AV. 
>

I can imagine that a book (if such a book actually exists) on designing
hearing aids would be of interest.

cheers

Am 17.12.12 12:18, schrieb aaab:
> I would like to get started on Multiband Amplitude Compression in
> the Frequency Domain. So basically I would like to do the processing
> like Compression of the signal on frequency spectra (bins).
>
> Can anybody suggest any links or references from where I could
> get an understanding of how can I do it ?

Postfish is an excellent audio processing software which includes a 
multi-band compander and is open source:

	http://svn.xiph.org/trunk/postfish/

Look into this file
	http://svn.xiph.org/trunk/postfish/multicompand.c

Unfortunately, it doesn't work on modern Linux boxes. I could get it 
compiled and running on an Ubuntu 8.04 virtual machine, though. It would 
be great to see an updated port to use it on modern OSes.

	Christian

On Tuesday, December 18, 2012 11:35:25 PM UTC-6, aaab wrote:

> I am seeking much more details in terms of 
> the core algorithm and sound pressure measurement to be used. 

I think you'll find that (1) there aren't very many, and (2) the few that do exist are proprietary and thus not much info is available about them.

Greg

On Monday, December 17, 2012 3:18:12 AM UTC-8, aaab wrote:
> Dear all, 
> 
> I would like to get started on Multiband Amplitude Compression in 
> the Frequency Domain. So basically I would like to do the processing 
> like Compression of the signal on frequency spectra (bins). 
> 

What is your motivation? (Answers to that, both personally and algorithmically may enable and motivate more useful responses.)

> 
> Can anybody suggest any links or references from where I could 
> get an understanding of how can I do it ? 
> 


http://www.rehab.research.va.gov/jour/93/30/1/pdf/kollmeier.pdf

http://www.ti.com.cn/cn/lit/an/spra657/spra657.pdf

http://nemertes.lis.upatras.gr/jspui/bitstream/10889/2391/1/ThesisSESE.pdf

http://ticet.iitb.ac.in/ticet/publications/Long%20Term%20Research%20Projects/kulkarni_pandey_jangamashetti_July09.pdf

Dale B. Dalrymple

Dear all, 

Thanks for your posts. I will refer to them and get back 
in case I have more queries. 

Regards,
AV.

Hi all, 

When I use different number of samples to do the fft, 
I get fft spectra values which are different in value. 
So say I have a tone at 1500 Hz at sampling frequency of 20000 Hz 
of 1 second duration. 
First I take only the first 512 samples and find the fft. 
Then I take only the first 1024 samples of the same input and 
find the fft. The maximum absolute value of these two ffts are found to be
different. 

Please let me know what can I do to ensure that fft spectra values can
be compared irrespective of the number of samples taken for fft (or window
length). 

Here is the sample Matlab code for illustration. 

For compression in the frequency domain I need to address this issue. 

>>t= [1:20000];s = 0.999 * sin(2 * pi * 1500/20000 * t);

>> s2 = s(1:512);   fft_s2 = fft(s2); plot(abs(fft_s2));

>> s3 = s(1:1024)); fft_s3 = fft(s3); plot(abs(fft_s3));

It is seen that max(abs(fft_s2)) is different from max(abs(fft_s2))
since number of samples are different. But I want to be able to compare or

get a relation between these values irrespective of the number of samples 
used for fft.

Thanks and regards,
AV