Emax

Hi,
The Emax uses a fixed rate sample replay algorithm and therefore drops/adds
samples, just like the SP's. However the E chip within the Emax is
considerably more complex than the TTL chip based micro controller in the
SP's, as it deals with different sample rates, as well as
compression/expansion of the samples. The Emax sample engine is good for
keyboards as it pitch shifts (down) reasonably well, the SP engine is for
drum samples where good quality pitch shifting is not important. The SP
sample replay engine is the same as the Drumulator, as are all the filters.

The E chip is only a basic DSP, and the SE sample manipulation features run
on the main processor. The E-chip is a custom DSP chip which manipulates 16
channels of digital audio. The chip performs three main jobs:

1)   It replays the samples from memory and pitch shifts them as necessary
using a fixed sample replay rate that adds and drops samples to achieve the
transposition in pitch. It understands the sample rate of the sample.

2) It translates the 8-bit samples that are held in sample memory back into
12-bit samples ready for conversion back into an audio signal.


3) It adjusts the volume of each individual sample as required by the patch,
although the final VCA is in the analog filter chip. Overall sample volume
and modulation from the LFO is set by the E-chip.

The Akai S950 (variable rate) and Emax have very different frequency
responses, with the Akai having 5dB boost from 3.5kHz to 21kHz, whilst the
Emax drops 9dB at 18kHz. The Akai has much less pitch shift distortion, but
the Emax distortion is due to the compression/expansion of samples more than
shifting, which also affects dynamic range. The E chip may also be over
sampling, but the precise design is confidential.

An Emax and SP do sound similar because they are much closer in design than
an E-mu and Japanese sampler. The technical specs of the Emax are inferior
to the Akai, but musicians often prefer the sound of the Emax.

Hope this helps!

Rob
www.emulatorarchive.com

 Strange. Everyone I know who's interested in the Emax, likes the way
the emax mangles samples during pitch shifting.  The draw is that
this is the closest thing to SP-12/1200 pitch shifting.

I don't know for sure, but I imagine the circuit for pitch shifting
in the SP is to simply repeat or drop samples as needed to produce
the required pitch change at a fixed sample playback clock.  This
would account for the square wave sound on top of the pitched SP
samples.  However, this requires no dsp power whatsoever, other than
an adder with some fractional precision.  So although all the other
stuff in the Emax might be complicated, I never imagined the pitch
shifting would be complicated.  Is that true?

BTW I have an S950 and the pitch shifting on it (not to be confused
with time stretching) is fine.  I never notice artifacts like on the
SP.


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