issue04

EMUSIC-L Digest                                      Volume 56, Issue 04

This issue's topics:
	
	1-bit sampling?? (4 messages)

Your EMUSIC-L Digest moderator is Joe McMahon .
You may subscribe to EMUSIC-L by sending mail to listserv@american.edu with 
the line "SUB EMUSIC-L your name" as the text.
 
The EMUSIC-L archive is a service of SunSite (sunsite.unc.edu) at the 
University of North Carolina.
------------------------------------------------------------------------
Date:         Sun, 12 Sep 1993 10:24:25 U
From:         David Williams 
Subject:      1-bit sampling??

Can someone explain what 1-bit sampling is all about, please.  I understand 8-,
12-, and 16-bit ADCs and DACs alright.  But, I notice now devices that claim
1-bit ADCs and I don't understand how this works.

Thanks for any help on this.

Dave Williams
Illinois State University

------------------------------
Date:         Sun, 12 Sep 1993 11:12:03 -0700
From:         Michael O'Hara 
Subject:      Re: 1-bit sampling??

Picture a car jack.  It can "notch" up, or down as needed. This is the basis
of one-bit sampling.  Obviously, in order to keep up with a fast moving signal,
you must crank that sucker REAL fast.

Now, unlike the car jack, we are always cranking in one direction or the other.
This means, that an unchanging signal level is going to be represented as a
sequence like up-down-up-down-up-down; exactly a 50% ratio. As the rate-of-
-change increases, the sequence deviates from 50% as required.

Advantages:
Little or no filtering required.
Comparitively simple circuitry. (sp)
As an ADC, very good group delay characteristics.

(overall an excellent performer)

Disadvantages:
Very fast components required; cutting corners in the comparater selection will
        compromise performance.
As a DAC, requires especially long "digital filters" for good pulse response,
        but can give better performance with no analog filtering at all req'd.

------------------------------
Date:         Mon, 13 Sep 1993 06:09:01 -0400
From:         Andy Farnell 
Subject:      Re: 1-bit sampling??

I believe that this type of 1 bit sampling is known as, amongst other names,
delta modulation.

As always I can recommend that fine text by K.Pohlman - Principles of Digital
Audio - which I am sure deals with the subject.

Andy Farnell
Computing and Cognition
ACE
Bournemouth University
England

------------------------------
Date:         Mon, 13 Sep 1993 13:27:42 UT
From:         Hutzenbiler Leroy 
Subject:      Re: 1-bit sampling??

Take, for example, a 4 bit sample.  The bit values are 1, 2, 4, & 8.  Instead of
converting each bit to a voltage, convert each bit to a charge and integrate to
a voltage.  Look at the bits in any order at a clock rate of most significant
bit value * the sampling rate ( e.g., 8 * 22,000).  If the '1' bit is on,
generate a constant voltage for one clock,  If the '2' bit is on, generate a
constant voltage for two  clocks, if the '4' bit is on, generate a constant
voltage for four clock cycles, and if the '8' bit is on, generate a constant
voltage for eight cycles.   The constant voltage generates a charge proportional
to the bit value.  Integrating converts to a voltage.  The advantage of this is
that one stable voltage and an accurate clock are easier to implement than a
voltage adder.  Oversampling is relatively easy, too.  In the example, a clock
rate of (4 * most significant bit value * the sampling rate) would give a 4x
oversampling.

    LeRoy

------------------------------
End of the EMUSIC-L Digest
******************************