[sdiy] FW: Kawai K3 - Bandlimited Waveforms

[Plutoniq9 •]

Well, the k3/km, I think, has a 72- note key range, 6 octaves hence the
6 interleaved waveforms it uses for every sound. I checked out the
sq-80 roms and they seem to take the same approach, a bandlimited wave
for each octave, except the sq-80 uses 512-byte wave for all the
octaves, on the k3 it halfs the sample resolution each octave you go
up, 512 for the lowest and 32 bytes for the highest two octaves.

As,
I think it was Paul, mentioned, the derivative is probably for a cheap
way to do linear interpolation.....the 8031 CPU was probably stretched
enough doing everything else (ie software envelopes, lfos etc).

I'm
trying to avoid having to do additive resynthesis to produce
bandlimited waves for it, mainly cause it's over my head how to
implement this into my program. I had pretty good results using a
really steep 32-stage low-pass filter prior to downsampling the master
512-byte wave to produce the other octaves, I haven't tested this
inside the k3 yet but it seems this might be the easiest approach (it's
the first thing mentioned when researching bandlimiting), maybe not the
best.

I actually like the lack of bandlimiting on the lower
octaves, the k3 almost seems to overdo it to the point where the waves
sound dull, most noticible on the square/saw waveforms, so I'll
probably make it so you can select the amount of anti-aliasing
filtering per octave.

Thanks for everyone's input, it's been a fun thread to read thru.

Ryan

p.s
I managed to disassemble the k3's firmware for the 8031 into assembley
language, I only understand c++ though but if anyone wants a look at
it, just send me an email. It was cool how Colin Fraser reworked the
super jx's firmware to accept midi cc for all parameters, something
like that or syncing the lfo would make a nice addition to the
k3.....inverted envelopes etc.

----------------------------------------
> Date: Sun, 17 Jan 2010 14:36:18 +0100
> From: rainer at buchty.net
> To: plutonique9 at hotmail.com
> CC: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] FW: Kawai K3 - Bandlimited Waveforms
>
> On Sun, 17 Jan 2010, Plutoniq9 • wrote:
>
>> I have a question, how come normal wavetable synths don't need to go
>> to this extent to reduce aliasing in the higher octaves (normally they
>> just use a single waveform right?) secondly.....
>
> Why do you think they don't?
>
> E.g. in the early Ensoniq synths the higher octaves get mapped towards
> octave and sine waveforms by the multisample zone table.
>
> Take the saw wave, for instance, which consists of the following 16
> sample zones (each spanning 8 keys, starting at MIDI key #0):
>
> fcb $34,$34,$34,$34,$34,$35,$36,$36,$37,$37,$38,$38,$39,$18,$16,$15
>
> Here, you have different limitations of the saw wave ($34-$39), $18 is a
> muffled version (saw2), $16 is a slightly distorted sine, $15 is plain
> sine.
>
> Also the multicycle waves (i.e. real samples) are usually made from 2-3
> sample zones.
>
> I didn't look closely into the K3's ROM yet, but maybe there's a similar
> zoning mechanism available.
>
> Rainer
 		 	   		  
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