analog storage sequencers

brad sanders brad.sanders at
Wed Mar 12 05:00:51 CET 1997

>> Hey, y'know what? This might be a PERFECT application of those ISD
>> "analog EEPROMs" we were talking about the other day...

  Eli Brandt sez...

>Six bits you could scale to get 64 semitones, if it's precise and linear.
>But I got the impression that these things aren't any kind of precise,
>so you'd have like half-semitone tracking error.  That would hurt.

Yes - except you can easily increase precision by *scaling* voltages.
Like I said: it takes no more than 1Vp-p input, so the voltages have
to be scaled anyway. Increase voltage division to give 1 octave
tracking and you have MAX freq. inaccuracy of a few cents.

Also, the steps aren't discretized; the voltage in each cell is
continuously variable (think of a moderate accuracy, infinitely
sustainable S/H circuit). These cells are cycled through at a fixed
(adjustable) rate. Given the higher sample rate (say, 11KHz) a 1KHz
low pass filter on the output means the output would be a weighted
"average" of the last several storage cells read. Unless there's some
weird process characteristic that makes these devices prone to DC
errors, one SHOULD be able to get pretty good tracking via this
"averaging" (Just as predicted by Nyquist).

Unfortunately I can't say for sure at this point - I can't find the
one and only sample I had around here.

To answer the other query on sources: These ARE NOT "EEPOTS" or
anything similar. They are "analog memories" (EEPOTS use digital
storage cells and interface circuitry). The one and only maker of them
(thus far) is a company called ISD. The chips are available through
radio shack, or through Digi-Key. I dunno if Digi-Key has info online
or not; perhaps ISD has a web site (but I doubt it - they're not too
"friendly" to little guys).

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