Radio Shack FX2 User Manual download pdf (Page 17)

E P S I n t e r n a l s : B o c k t o t t i e B a s i c s

The EPS 16 Bit Myth

There's quite a few myths ﬂoating around about the EPS.

Myths like Ensoniq created their original EPS samples on a six

teen bit development system, so those old disks will play back

as sixteen bit samples on an EPS-16 Plus. Or the EPS can play

EPS-16 Plus disks with improved ﬁdelity over EPS sounds.

With this confusion ﬂowing around, it's time to throw my own

two bits in.

Sample resolution is deﬁned by the number of bits containing

the information. A bit has only two values, 0 or 1. Two bits can

store the information 0, 1, 2 or 3. Three bits can store the infor

mation 0, 1, 2, 3, 4, 5, 6 or 7. Remember this last sentence, be

cause there's gonna be a test later. Every new bit doubles the

storage capacity, so at 13 bits you get 8192 points of informa

tion, and at 16 bits you get 65,536 points, or 8 times as many.

That, and only that, being the difference between 13 and 16 bit

samples, where did these misconceptions arise about the EPS?

Most of it comes from inaccurate interpretations of Ensoniq's

own speciﬁcations, which have a tendency to be vague at

times.

The EPS Musician's Manual speciﬁcations give a data storage

format of 16 bits and a sample converter resolution of 13 bits.

From this information you might incorrectly deduce that 16 bit

ﬁles can be saved on an EPS if the Analog to Digital converters

are bypassed.

Well, it's true that the EPS stores samples to disk in a sixteen

bit ﬁle format. It's also true that transfers between computer

and EPS over MIDI o r S C S I u s e a s i x te en bit for m a t . That's

why disks and software for the EPS are compatible with the

EPS-16 Plus. So isn't the EPS 13 bit Analog to Digital con

verter for user sampling the limiting component in this instru

ment? Nope! The real culprit is the EPS memory. The EPS

internal RAM storage capacity is 256k words x 13 bits, and the

port for expansion memory is only 13 bits wide as well. It

doesn't matter whether EPS samples are done using the internal

Analog to Digital converter, or transferred via MIDI or SCSI, if

the RAM's only 13 bits wide then the lowest three bits will get

truncated before the sample is ever saved to disk.

This works both ways. If you load an EPS-16 Plus disk into the

EPS, the lowest 3 bits of every 16 bit sample word get lost, be

cause there's no RAM locations for those bits to get stored in.

You'll still be playing 13 bit samples, though it's possible the

higher ﬁdelity of the EPS-16 Plus input sampling stages might

improve the sound somewhat.

If you own a computer with sample editing software and an

EPS-16 Plus this 13 bit limitation of EPS samples is easy to

verify. Load in an Ensoniq or other computer developed EPS

sample from the 16 Plus over MIDI or SCSI and save the ﬁle to

John Lojﬁnk

disk. Now load the ﬁle into a binary ﬁle editor (there are many

available in the public domain), ignoring the ﬁrst ten or twenty

lines which probably contain various sample parameters.

Here's a section from one such sample:

02F0: FE90 2690 1728 FFA8 E7F8 C650 D990 F7E8

0300: 0628 0328 0950 IDDO 2650 EF40 D950 14F0

0310: 15D0 ECA8 FA40 10A8 1728 2FE8 10F8 E280

The ﬁrst four character segment is the address or location for

the line. The rest of the four character segments are the actual

data, where each character represents a four bit word in what is

called hexadecimal format, and each segment represents a 16

bit sample word. Did you notice how the last digit is always an

8 or a 0? This is because the lowest 3 bits of the sample are al

ways zero. There's no 0 through 7, just 0 or 8. Because the last

character has only two values, it represents a resolution of 1 bit.

Each segment has an actual resolution of 4 + 4 + 4+1 bits =13

bits.

Looking at it another way, the samples consist only of the

decimal values 0, 8, 16, 24, 32, 40...65536. This gives the ac

tual number of points as 65536 divided by 8, which is 8192, the

resolution for 13 bit samples.

The above sample data is taken from the instrument "Crystal

Bell" from the original Ensoniq disk #ESD-4, one of the ﬁrst

EPS disks released by Ensoniq. While it was possible that En

soniq could have rigged special 16 bit EPS's for their sample

development, a random examination of their original disks

shows that this is not the case. Sixteen bit development system

or not, Ensoniq's own EPS samples are thirteen bits just like

everyone else's.

There's just one way to get 16 bit samples and the ﬁdelity as

sociated with them: develop and play them on a 16 Plus. ■■

References:

"Inside the EPS" by Dick Lord, Transoniq Hacker #39, Sep

t e m b e r 1 9 8 8 .

"Ensoniq EPS-16 Plus Digital Sampling Workstation"

(reviewed by Gary Hall), Electronic Musician, April 1991.

"EPS-16 Plus" (letter by Mick Seely, Livewire Audio),

Electronic Musician, ivily 1991.

Bio: John Lofﬁnk owns and operates First Generation, a

source for computer synthesized EPS & EPS-16 Plus samples,

He has just ﬁnished converting 60+ samples from 13 to 16 bits,

and needs a vacation.

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