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Re: 3D Audio -improving HRTF filtering

Hi Fred,

Off course, any kind, is that I wanted to say (or rectangular windowing, that is the same).

Windowing is indicated for signal analysis and other DSP things, but not for fast convolution using FFT.


----- Original Message ----- From: "Fred Herzfeld" <herzfeld@xxxxxxxxxxxx>
To: "Jose Javier Lopez" <jjlopez@xxxxxxxxxxx>
Sent: Wednesday, April 05, 2006 7:15 PM
Subject: Re: 3D Audio -improving HRTF filtering

Hi Jose,

I agree that a Kaiser window should not be used, in fact for any kind of accurate results no window at all shoud be used. Why did you single out Kaiser?


Jose Javier Lopez wrote:
Do not window input samples with kaiser !!!!!!!!!!!!!!!!!!!

Review overlap-add or overlap-save algorithm in "Oppenheim - Distrece-Time Signal Processing".

or look for code examples on Internet.


----- Original Message ----- From: "sherin tech" <sherin.tech@xxxxxxxxx> To: <AUDITORY@xxxxxxxxxxxxxxx> Sent: Wednesday, April 05, 2006 11:38 AM Subject: [AUDITORY] 3D Audio -improving HRTF filtering

Hi all,

I am working on 3D-Audio based on HRTF filtering.

My starting point is KEMAR data from MIT media labs, done by bill
gardner and Keith Martin.

I have implemented a basic by referering to the demo SGI code provided
in MIT site.

My first implementation is just time domain convolution , which works
wothout any noise.

But for efficient implementation I am trying to move to frame based processing, as in the SGI code provided in the MIT website.

the steps involved in my new implemantation are ...

1) take 1024 number of samples.
2) Window those 1024 samples. (for this I am now using kaiser window of beta=16)
3) Take 1024 point FFT the input
4) Zero pad the 128 point HRTF filter to make it 1024 point.
5) Take 1024 FFT of HRTF Left ans Right data.
6) Multiply the spectrum in frequency domain.
7) Take 1024 point IFFT of the resultant spectrum.
8) Do a 75 % overlap and add.

But a minor amout of noise is present in the o/p ....

As a general instruction ... how can I improve the SNR of the o/p ?????

I have tried , diferent type of windows, and overlap of 50 % also ..

Any lights in to this ... ????


Fred Herzfeld, MIT '54
78 Glynn Marsh Drive #59
Brunswick, Ga.31525