[music-dsp] DSP vs analog circuits

James Chandler Jr jchandjr at bellsouth.net
Mon Oct 15 16:14:47 EDT 2001


>>> Umm, guys... they allready do this....Digital filtering...  Active
filters
> are made with opamps, caps and resistors mostly.  They can do that in
> digital quite efficiently and more effectively than most analogue filters
> now adays.

Hi, Jared

Yeah, there are usually equivalent ways to get analog tasks done in DSP,
though the strategies are often quite different.

Was just pointing out that opamp (or feedback in general) is a very useful
trick that is pretty difficult in DSP.

EQ is one of many cases... Using a bank of parallel analog filters in the
feedback loop of an opamp, it is quite easy to get symmetrical constant-Q
Boost-Cut behavior.

In the closest DSP EQ equivalent of a parallel filter bank, the Cut
percentage bandwidth is narrower than the Boost percentage bandwidth.

One can get symmetrical Boost-Cut DSP EQ behavior with a bank of series
peaking filters, however. Just a different approach to the problem.

Some DSP equivalents seem more problematic. A really useful analog feedback
technique, for steeply supressing harmonics on a signal-- Make the
equivalent of a backend-sensing compressor, except you substitute a steep
tracking lowpass filter for the usual wide-band tracking gain element.

I've tried this tracking filter trick in DSP, and the result is not as
satisfactory (at best marginally useful). A smarter programmer could
probably get it to work better (G).

James Chandler Jr
jchandjr at bellsouth.net
http://www.mp3.com/mikrodotz





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