[sdiy] FW: Kawai K3 - Bandlimited Waveforms

[Paul Maddox]

Karl,

 :-)
Good question....

the answer is not really, but sort of...

The PPG uses a 20bit control register and a 24 bit accumulator.
the control register is added to the 24 bit accumulator 250,000 times a second.
the top 7 bits of the accumulator are used to drive the lowest 7 bits
of the ram address bus.

I hope this helps

Paul

2010/1/18 karl dalen <dalenkarl at yahoo.se>:
> Do the PPG realy use a variable clock as you have drawn?
> Are the variable clock a phase acc from wich PPG has taken
> the msb to clock the counters with?
> http://www.electricdruid.com/index.php?page=info.wavetableoscs
>
> KD
>
> --- Den mån 2010-01-18 skrev Tom Wiltshire <tom at electricdruid.net>:
>
>> Från: Tom Wiltshire <tom at electricdruid.net>
>> Ämne: Re: [sdiy] FW: Kawai K3 - Bandlimited Waveforms
>> Till: "karl dalen" <dalenkarl at yahoo.se>
>> Kopia: synth-diy at dropmix.xs4all.nl
>> Datum: måndag 18 januari 2010 03.53
>>
>> On 17 Jan 2010, at 22:34, karl dalen wrote:
>>
>> > Its interesting to note that the K3 does a poor job in
>> this
>> > sample table per octave switching, one can very easily
>> hear
>> > when a table are swapped in and out.
>>
>> They didn't use any interpolation between adjacent
>> wavetables then.
>> As we've already discussed, they did interpolate between
>> wavetable samples, but it looks like that was it.
>>
>> > Btw, should phase accumulator NCO's be wieved as
>> > variable sample rate or fixed rate NCO's?
>> >
>> > I was thinking of the aliasing on an NCO using low
>> rate
>> > versus one that uses a high rate (1Mhz or more).
>>
>> Well, this is where the confusion arises.
>>
>> I'd say (and this is an opinion not a statement of fact)
>> that if it's got a "high" sample rate and "small" tables,
>> then it can be viewed as a variable sample rate system. At
>> least, it approximates one. This is the PPG scheme. In a
>> system like this, each individual wavetable sample is
>> typically repeated many times, which is roughly equivalent
>> to clocking the samples out at a much slower, variable rate.
>> In practice, the line blurs, since at the top of the PPG's
>> range, it starts missing samples out because the sample rate
>> isn't high enough (only 250KHz).
>>
>> Obviously the reality is that both systems have a fixed
>> rate, and it's purely a way of viewing it.
>>
>> T.
>>
>>
>
>
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