Forums

Equalization using DFT

Started by jungledmnc November 12, 2008
> > >> 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