[Elecraft] Quantization noise and DSPs

Sat May 10 12:32:00 2003

For those interested in DSP, the following link from Analog Devices is a
very good primer on the technology:

http://www.analog.com/Analog_Root/static/technology/dsp/beginnersGuide/intro
duction.html

In reference to quantization noise, there are more serious limiting factors
once you reach a true 16bits in the codec.  External noise, grounding,
cabling, resistive thermal noise, external audio transducers, etc all come
into play.

There are other papers on Analog's website that discuss DSP limitations like
24 vs 16 bit codecs and 32bit vs 24bit processors (internal floating point
significant digits).  I also found some papers on Dolby SR noise reduction
that demonstrate wider dynamic range (in recording) using analog tape than
DAT 48khz 16bit.

If you have a copy of MATLAB, the filter design tool enables you to graph
the quantization effects of 16, 24 etc. bits.

Jerry Hancock, KG6KGP

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of James R. Duffey
Sent: Friday, May 09, 2003 6:07 PM
To: [email protected]; [email protected]
Subject: [Elecraft] Quantization noise and DSPs

Bill - I have one of the original W9GR DSPs. In my experience, it is not
possible to hear the quantization noise of the analog to digital (A/D)
converter. There are other digital artifacts though, some clock feed through
is noticeble on very quiet bands and the artifacts from the noise reduction
and voice enhancement are also evident in an A/B comaprison.

The noise introduced by quantization in a perfect analog to digital
converter is the least siginificant bit (lsb) divided by the square root
of 12. In practical use without AGC, one tends to put the noise level at
several bits, which is far above the quantization noise introduced by the
A/D converter.

8 bits are enough dynamic range for CW signals, but without AGC, it does
require some riding of the volume control. I also have DSPs with 12, 16, and
24 bit A/Ds as well, some with AGC, but only the 24 bit DSP can ignore the
volume control.

All in all I have more audio filters than I can recall; collecting them is a
bad habit of mine. My favorite CW filter is an analog one, the DaTong FL-3.
My favorite DSP for CW is made by Zim, VK3GJZ, with 24 bit CODEC it sounds
like an analog  filter with no detectable digital artifacts. See:

<<http://www.users.bigpond.com/gzimmer/Alesis.html>

for more information on Zim's filter.  My favorite overall DSP is the
Timewave 59+, but the DaTong is a close second. In my experience, DSP is not
of as great a utility in CW as it is for voice or data. I have not noticed
the delay mentioned by Andrew on the 59+ or Zim's filter, but I do not
operate high speed CW except on contests. I have noticed it on the NIR-12
though, which was unexpected.

I have not seen or heard the K-2 DSP, so I cannot comment on it. I expect
that its greatest utility will probably be to eliminate heterodynes on SSB
and as a  filter for data signals. I have heard and used the K2 with the
KAF2, which is a good sounding combination on CW, even at the narrow
setting. I suspect that most K-2 CW only ops will think the DSP overkill.
Now, if you operate SSB on 40 M after dark, the DSP will be a godsend. - Dr.
Megacycle KK6MC/5
______________________
James R. Duffey KK6MC/5
Cedar Crest NM 87009 DM65

t

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