Super filter No filter

[Mikko Helin]

Regarding "digital sawtooth" production, you could use combined sampling
and "virtual synthesis" so that you use sampled saw retrace and
combine it with a calculated raising part of saw. Usually the saw retrace
is fixed (cap recharging via scmitt trigger). This way there
will be no aliasing (-Should I patent this method?). 

Another way to simulate analog filter digitally would be to
look for the patterns in waveform and try to generate alike
(looking) waveform. This kind of "virtual synthesis"
doesn't need any mathematical models like FFT and such
based on harmonics or additive synthesis, and you are free to use 
any kind of wave modelling functions and even sampling.

If you want digital filters look into Hal Chamberlin's
book, there's a digital model of state-variable filter,
which needs only two or three multiplications/sample.
A saw VCO and filter like this could easily be fitted on
PIC16C71 or similar micro with multiplication instructions,
or you could even use one without multiplication if
it's fast enough (say Scenix).

-Mikko

Btw. Could the additive synthesis no-filter filter use
non-integer harmonics to capture the non-harmonic response
of a resonent filter?

 
>If you are going to process only a "digital sawtooth", you just need
>sinewaves to satisfy the the 'recipe' for a sawtooth, i.e. F(a) + 2F (1/2a)
>+3F (1/3a)... until you leave the audio spectrum. No "filters" at all are
>needed. These sinewaves would all be in phase, and your "filter" algorithm
>would reduce the amplitudes progressively from the maximum.
>
>But (caveat) you can't simulate the non-harmonic response of a resonant
>filter.
>A low-pass is easy, but those "in-between" points where the harmonic is
>almost at a peak won't sound the same.  
>
>The "ladder" is out of patent by now, isn't it.  Analog Rules!!!    Harry
>Bissell
>
>> -----Original Message-----
>> From:	Guido Goebertus [SMTP:guidogoe at xs4all.nl]
>> Sent:	Wednesday, March 03, 1999 3:17 PM
>> To:	synth-diy at mailhost.bpa.nl
>> Subject:	Super filter No filter
>> 
>> Gene wrote:
>> 
>> >List,
>> >
>> > A recent thread about waveform synthesis reminded me of an  idea I had
>> >about 25 years ago when I was into synths. I wanted to build a single
>> >voice channel (ala Moog).
>> 
>> You could still use the vocoder idea. I thought this over for as many
>> years. (Well, almost:-).
>> You'll need to program a DSP with a lot of bandpass filters if you want to
>> do this digital. You'll also need a (digital) sawtooth to process.
>> This, to my knowlegde hasn't been done before to process a single voice.
>> But it would certainly sound very different compared to additional
>> synthesis, because it  is still subtractive, like analog synths.
>> I am working on this right now, but analog for the moment.
>> Maybe later I decide to programm my DSP-board.
>> 
>> Regards, Guido