Re: 3D Audio -improving HRTF filtering (sherin tech )


Subject: Re: 3D Audio -improving HRTF filtering
From:    sherin tech  <sherin.tech@xxxxxxxx>
Date:    Thu, 6 Apr 2006 13:56:21 +0530

hi fred & Jose, So, If I am using rectangular window, ie, just taking M samples with a hop size of again M. for filtering using 128 point ( L ) filter ... I have to take Nfft >= M+L-1 i took, Nfft as 1024 ... and after the convolution I get back 1024 time samples .. which, I am doing a 50% overlap and add with the previous 1024 samples .. I am getting the o/p without any noise .. Can we avoid this overlap and add ?? (i don't think) regards, sherin On 4/5/06, Jose-Javier Lopez <jjlopez@xxxxxxxx> wrote: > 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. > > JJ > > > ----- Original Message ----- > From: "Fred Herzfeld" <herzfeld@xxxxxxxx> > To: "Jose Javier Lopez" <jjlopez@xxxxxxxx> > 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? > > > > Fred > > > > 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. > >> > >> JJ > >> > >> > >> ----- Original Message ----- From: "sherin tech" <sherin.tech@xxxxxxxx> > >> To: <AUDITORY@xxxxxxxx> > >> 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 ... ???? > >> > >> regards, > >> sherin > >> > >> > >> > > > > > > -- > > Fred Herzfeld, MIT '54 > > 78 Glynn Marsh Drive #59 > > Brunswick, Ga.31525 > > USA > > >


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Electrical Engineering Dept., Columbia University