Equalization using DFT

>
> >> I'm wondering, if there is no problem in equalization with DFT. Simply
> >> window �the source signal, DFT, mutliply each frequency bin by a real
> >> value
> >> defining it, and IDFT. This would even be zero-phase filtering
> >> wouldn't it?
>
> >


to the OP...

there are two common usages for the term "equalization" or EQ

Are you taking about:

1) EQ as in audio where you want to taylor the frequency response, i.e
fancy tone controls

or

2) EQ as in an adaptive equalizer  where a digital demod is
compensating for linear distortions in a channel?

Mark

>to the OP...
>
>there are two common usages for the term "equalization" or EQ
>
>Are you taking about:
>
>1) EQ as in audio where you want to taylor the frequency response, i.e
>fancy tone controls
>
>or
>
>2) EQ as in an adaptive equalizer  where a digital demod is
>compensating for linear distortions in a channel?
>
>Mark
>

Well, I mean the audio related stuff.

dmnc

jungledmnc wrote:
(someone wrote)

>>2) EQ as in an adaptive equalizer  where a digital demod is
>>compensating for linear distortions in a channel?

> Well, I mean the audio related stuff.

How about a box with stereo line in/line out that would fit
in with the rest of an audio system.  Also with USB or ethernet
so one could connect to it and load new programs.

It would have A/D converters on the inputs, D/A converters
on the outputs, and a completely programmable DSP in between.

A front panel with some LEDs that the DSP could also control
might be nice.   Maybe some front panel switches to select
between previously loaded programs, such as different
equalization curves (implemented as separate DSP programs).

-- glen

Glen Herrmannsfeldt wrote:
> jungledmnc wrote:
> (someone wrote)
> 
>>> 2) EQ as in an adaptive equalizer  where a digital demod is
>>> compensating for linear distortions in a channel?
> 
>> Well, I mean the audio related stuff.
> 
> How about a box with stereo line in/line out that would fit
> in with the rest of an audio system.  Also with USB or ethernet
> so one could connect to it and load new programs.
> 
> It would have A/D converters on the inputs, D/A converters
> on the outputs, and a completely programmable DSP in between.
> 
> A front panel with some LEDs that the DSP could also control
> might be nice.   Maybe some front panel switches to select
> between previously loaded programs, such as different
> equalization curves (implemented as separate DSP programs).
> 

It's been done:

http://chameleon.synth.net/english/index.shtml

but hardware supply has just about ground to a halt (uneconomic), though 
the user community is still very active.  Line6 have developed a dsp 
development plugin module  (Freescale-based)  for their modular 
"ToneCore" footpedal system. No MIDI  though, which limits it as a 
general-purpose development system.

But the canonical route these days is to develop software plugins using 
variously VST, AudioUnits, DirectShow, in order of popularity.


Richard Dobson

Richard Dobson wrote:
(snip, I wrote)

>> How about a box with stereo line in/line out that would fit
>> in with the rest of an audio system.  Also with USB or ethernet
>> so one could connect to it and load new programs.

>> It would have A/D converters on the inputs, D/A converters
>> on the outputs, and a completely programmable DSP in between.

>> A front panel with some LEDs that the DSP could also control
>> might be nice.   Maybe some front panel switches to select
>> between previously loaded programs, such as different
>> equalization curves (implemented as separate DSP programs).

> It's been done:

> http://chameleon.synth.net/english/index.shtml

Pretty neat.  Though I meant one more oriented for
home use than professional studios.  The price
(and feature set) would be smaller, but the potential
market much larger.

-- glen


> but hardware supply has just about ground to a halt (uneconomic), though 
> the user community is still very active.  Line6 have developed a dsp 
> development plugin module  (Freescale-based)  for their modular 
> "ToneCore" footpedal system. No MIDI  though, which limits it as a 
> general-purpose development system.
> 
> But the canonical route these days is to develop software plugins using 
> variously VST, AudioUnits, DirectShow, in order of popularity.
> 
> 
> Richard Dobson

Glen Herrmannsfeldt wrote:
..
>> It's been done:
> 
>> http://chameleon.synth.net/english/index.shtml
> 
> Pretty neat.  Though I meant one more oriented for
> home use than professional studios.  The price
> (and feature set) would be smaller, but the potential
> market much larger.
> 


It's not really aimed at pro studios, but home studios, gigging groups 
who fancy the challenge, and hobbyists, and the increasing number of 
amateur VST programmers (in the sense of those who distribute them 
mostly as freeware via forums such as KVR)  who want to get into 
hardware given the tools. It a very variegated market out there these 
days. Conventional pro studios will not be interested in devoting lots 
of time to designing algorithms on the offchance some client will want 
to use them. I don't know how many Line6 ToneCore kits have been sold, 
that would be an interesting statistic.

The difference with Line6 is that they have a large established product 
line into which ToneCore literally plugs, so their bottom line is not 
dependent on dsp kit sales. With the Chameleon it was a small company 
with a single product  with high overheads, and they sold some 500 
systems (according to the info on their forum). Now maybe a product at a 
lower price point would sell more, but the Chameleon was really about as 
small a system, in useability and stage-performance terms, as one would 
want to devote a lot of energy to.  I resisted because I wanted more 
audio channels  (being interested in surround sound), and ideally 2 dsp 
chips to stand a chance of making a phase vocoder at a decent sample 
rate). That was going to be the Mark II model, but they cancelled  it 
for lack of resources.  The proportion of  kitchen-table VST programmers 
who would like to try hardware dsp is still likely a small proportion of 
the whole.

At the truly "pro" end of the market, one can get developer status for 
Digidesign pro Tools for free if one can prove competence and clear 
product plans - but the HD hardware is far from cheap.  The developer 
kit for the Creamware Pulsar/Scope platform (multiple Sharc dsps) is 
very expensive (last I heard, �10000), so clearly not aimed at hobbyists 
at all. That puts the Chameleon into some sort of context, anyway.

Richard Dobson