Elektron Musical Instruments

what does the term "phase accumulated" mean? 
i have seen it in reference to the Sidstation's oscillators but
have no idea what it refers to. anyone? 
cheers,
wendell.

> what does the term "phase accumulated" mean? 

Well, phase accumulated generally refers to the fact that an
index into a wavetable is used to play back a sample.  For a 
given frequency, there will be a delta which is added at some
regular time interval (e.g. 1/44100 s) to the current index into
the wavetable, and that sample is played through a D/A conv.

In most typical wavetable players (e.g. mod players, many non- analog
emulation synths and more), some extra computation/dsp work is performed
on the sample data.  This is to account for many things which are
just barely on the edge of my understanding.  But, basically, it has
to do with playing back wavetables at too slow of a rate.  For example, a 
waveform could have overtones in it that go above the Nyquist
rate when hte sample is played at a sufficient pitch.  Therefore, you've
go to filter them out, or suffer aliasing.

However, people often describe the sid as "phase-accumulated" instead of
wavetable in order to refer to the SID's superior synthesis method.  What
is so special about it?  Nothing, except two things: 1) the waveforms
are not stored in memory somewhere.  They are generated based on the
index (I believe it's a 12-bit accumulator?) and sent to D/A converters.
That alone is not such a big deal, it just means the SID doesn't require
external waveform memory, however, when you combine it with the other
superiority, it's important.  

2) The waveform generators in the SID are
generated (I believe) at 1MHz.  (Someone please correct me if I goof
on the exact value here )  Therefore, even the highest frequency sounds
that you're going to generate will not generate neigh imperceptible
amounts of aliasinhg distortion.

e.g. a 20KHz Sawtooth wave, which has a frequency spectrum roughly
equal to 1/h, which h is the harmonic number.  The Nyquist rate for a 
1MHz plyaback rate is 500KHz.  500KHz/20Khz=25.  The magnitude of that 
frequency, and those beyond it, is between 3 and 4 % of the fundamental's
amplitude.

Hope I got that right,
-N

> i have seen it in reference to the Sidstation's oscillators but
> have no idea what it refers to. anyone? 
> cheers,
> wendell.
> 
> 
> 
>  
> 
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ 
> 
> 
>

wow : )  are you working with elektron ??

lets start a STARTUP  company  !!!   i have a program that says "learn c c++ 
in 5 days "   : )

will make  synthesizers (soft/hard) with waves with totally different values 
!!!
LETS  CHANGE  THE MARKET !!!!
even the SIDSTATION became a "best-seller"  and uesed on several monster 
hits !! (log to sidstation.com  /sounds
hear >> zombie nation , sandman psychotoons  etc...  to understand !!! : )

or i'll just fligh to moscow (again)and look for old KGB synths  hehehe
cheers
izik sandman

--------------------
its a dog eat dog world out there , but from where i stand there aint enough 
DAMN DOGS



>From: shifty@...
>Reply-To: elektron-users@yahoogroups.com
>To: elektron-users@yahoogroups.com
>Subject: Re: [elektron] phase accumulated...
>Date: Thu, 24 May 2001 16:13:45 -0400 (EDT)
>
>
> > what does the term "phase accumulated" mean?
>
>Well, phase accumulated generally refers to the fact that an
>index into a wavetable is used to play back a sample.  For a
>given frequency, there will be a delta which is added at some
>regular time interval (e.g. 1/44100 s) to the current index into
>the wavetable, and that sample is played through a D/A conv.
>
>In most typical wavetable players (e.g. mod players, many non- analog
>emulation synths and more), some extra computation/dsp work is performed
>on the sample data.  This is to account for many things which are
>just barely on the edge of my understanding.  But, basically, it has
>to do with playing back wavetables at too slow of a rate.  For example, a
>waveform could have overtones in it that go above the Nyquist
>rate when hte sample is played at a sufficient pitch.  Therefore, you've
>go to filter them out, or suffer aliasing.
>
>However, people often describe the sid as "phase-accumulated" instead of
>wavetable in order to refer to the SID's superior synthesis method.  What
>is so special about it?  Nothing, except two things: 1) the waveforms
>are not stored in memory somewhere.  They are generated based on the
>index (I believe it's a 12-bit accumulator?) and sent to D/A converters.
>That alone is not such a big deal, it just means the SID doesn't require
>external waveform memory, however, when you combine it with the other
>superiority, it's important.
>
>2) The waveform generators in the SID are
>generated (I believe) at 1MHz.  (Someone please correct me if I goof
>on the exact value here )  Therefore, even the highest frequency sounds
>that you're going to generate will not generate neigh imperceptible
>amounts of aliasinhg distortion.
>
>e.g. a 20KHz Sawtooth wave, which has a frequency spectrum roughly
>equal to 1/h, which h is the harmonic number.  The Nyquist rate for a
>1MHz plyaback rate is 500KHz.  500KHz/20Khz=25.  The magnitude of that
>frequency, and those beyond it, is between 3 and 4 % of the fundamental's
>amplitude.
>
>Hope I got that right,
>-N
>
>
> > i have seen it in reference to the Sidstation's oscillators but
> > have no idea what it refers to. anyone?
> > cheers,
> > wendell.
> >
> >
> >
> >
> >
> > Your use of Yahoo! Groups is subject to 
>http://docs.yahoo.com/info/terms/
> >
> >
> >
>

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