source file: m1403.txt
Date: Sun, 3 May 98 11:34 BST-1

Subject: Re: JI Tuning Resolution

From: gbreed@cix.compulink.co.uk (Graham Breed)

Gary Morrison wrote:

>> While I'm plugging the AWE64...  You can set a Sound Font with
>> instruments in 88CET fairly easily.  You need one zone for each
>> run of notes with equal steps.
>
>   I'm glad to hear you're using 88CET!  :-)

Hang on, I said you _can_ get 88CET, not that I was doing this!
Actually, before I got pitch bend tuning working with the sample
editor, i was playing with 88CET and the best approximation to
29-equal, on the "anything rather than 12" principle.

>    But I did want to ask something kinda embarrassing:  I can't for the
> life of me seem to remember what "AWE64" refers to!  It seems like I used
> to know that, but I can't place it.  Is that a PC sound card perhaps?

To your last question, yes.  It stands for "Advanced Wave Effects
64 note polyphony."  It uses an EMU8000 chip, so has all the
advantages of that family, but unfortunately no tuning tables and
no real time control of filters.

Sound Fonts are an Emu standard for wave samples thayt they hope
to become an industry standard.  There's a "Scale Tune"  parameter
that sets the interval between notes, and this can be used to get
88CET.  Unfortunately, it can only take cent values so it's
useless even for a piano tuner's octave.  If you think this is
stupid, try writing to soundfont@emu.com and telling them so.

The one like Dave Rybarczyk plans to write software to retune a
Sound Font to a whole keyboard scale with cent step precision.
I'm hoping he'll find the time by the end of the year.  Otherwise,
I might have to do it myself!


John Loffink wrote:

> Synths frequency resolution is ultimately limited by hardware, which is
> specified in Hertz rather than cents due to the nature of the phase
> accumulator used in all wavetable/DSP synths and samplers.  A lookup table
> is used by the software that converts cents to Hertz (actually the phase
> increment), either one master octave or the whole keyboard.  This table
> might be stored in the synth manufacturer's custom integrated circuits or
> in their software code ROM.  Due to the speed requirements and low math
> capabilities of the main microprocessors it is unlikely that an algorithm
> would be used.

I'm sure a 16-bit processor can get 0.1 cent precision with
frequencies in an efficient way.  If there's enough memory for a
1536-TET tuning table, linear interpolation should only require an
8-bit multiplication and addition.  If this takes a sizeable chunk
out of the 0.3ms response time, I see no problem with doing the
interpolations in a quiet moment after all the notes have been
turned on.  Or, accurate frequencies could be calculated when the
table is loaded, at the expense of pitch bends.

The real reason we only get 1 cent precision must be that the
manufacturers think this is all we want.  The Sound Font blurb
implies this.


                    Graham Breed
      gbreed@cix.co.uk        www.cix.co.uk/~gbreed/