From: barry threw ()
Date: May 9, 2008
Subject:
Re: FAQ is BAQ! - frequency shifting.
A pd Hilbert.
bt
#N canvas 343 69 601 314 12;
#X obj 105 92 biquad~ 0.83774 -0.06338 0.06338 -0.83774 1;
#X obj 105 66 biquad~ 1.94632 -0.94657 0.94657 -1.94632 1;
#X obj 86 149 biquad~ -0.02569 0.260502 -0.260502 0.02569 1;
#X obj 86 175 biquad~ 1.8685 -0.870686 0.870686 -1.8685 1;
#X obj 86 39 inlet~;
#X obj 105 121 outlet~;
#X obj 86 202 outlet~;
#X text 34 232 This is a pair of 4th-order all-pass filters whose
outputs
somehow manage to be about 90 degrees out of phase from each other.
Both have different phases from the original. Adapted from a 4X patch
by Emmanuel Favreau \, circa 1982;
#X obj 502 39 inlet;
#X text 461 13 bang to clear;
#X text 80 16 signal in;
#X msg 502 112 clear;
#X connect 0 0 5 0;
#X connect 1 0 0 0;
#X connect 2 0 3 0;
#X connect 3 0 6 0;
#X connect 4 0 1 0;
#X connect 4 0 2 0;
#X connect 8 0 11 0;
#X connect 11 0 1 0;
#X connect 11 0 0 0;
#X connect 11 0 2 0;
#X connect 11 0 3 0;
On May 8, 2008, at 12:36 PM, Charles Henry wrote:
> On Thu, May 8, 2008 at 12:10 PM, robert bristow-johnson
> wrote:
>
>> there is a technical value judgement here ("best, simple[st],
>> [most] efficient, clean[est]") that might not be universally held.
>> another method that is current (even more current because in
>> Weaver's day, they didn't have real-time Hilbert transformers)
>> involves a single "filter" (the Hilbert transformer, i won't count
>> the corresponding delay line as another filter) and two sine/cosine
>> multiply operations. a quick Google search finds this link to
>> illustrate:
>>
>> http://www56.homepage.villanova.edu/scott.sawyer/fpga/II_frequency_shifting.htm
> [EMAIL REMOVED] >
> Quick question, here. I have sometimes struggled to create a good RT
> Hilbert transform (I made a couple of pd patches that while appearing
> to be correct on the surface with relevant math behind it, but
> produces horrible phase shifts). How does one make an RT Hilbert
> transform?
> (I can also provide details on my method, if desired.)
>
> Chuck
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barry threw
Media Art and Technology
San Francisco, CA
Work: 857-544-3967
Email: bthrew (at) gmail (dot) com
Web: www.barrythrew.com
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