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From: Rajkumar.R on 14 Jan 2010 03:41
Its clear about the filter banks, but i can not understand what does
the term DFT modulated means here. Can any one explain me please.
From: Chris Bore on 14 Jan 2010 13:47
On Jan 14, 8:41 am, "Rajkumar.R" <rraj...(a)gmail.com> wrote:
> Its clear about the filter banks, but i can not understand  what does
> the term DFT modulated means here. Can any one explain me please.

I do not know what is the context of the original discussion, but I
can imagine this arises for example in MPEG audio compression?

Here, the signal is divided into sub bands by filter banks. Then the
DFT of a segment of the signal is taken, and a quantisation is applied
to each bank based on the signal power in that band (measured by the
DFT) and a psycho-acoustic model of perceptive hearing (expressed in
frequency domain). In the case of MPEG, use is made of the idea that a
'desired' signal in a sub band 'masks' noise in that sub band - thus
the signal can be more roughly quantised in that band (which
introduces quantisation noise in that band, which is masked by the
signal..).

One way to quantise the bands would be to multiply (modulate) each
band by the reciprocal of the signal energy in that band, and so the
term 'DFT mpodulated filter banks' might be used.

Chris
=====================================
Chris Bore
BORES Signal Processing
www.bores.com
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