modulation: audio DC offset

On 12/25/2009 10:38 AM, Jerry Avins wrote:
> Muzaffer Kal wrote:
>> On Thu, 24 Dec 2009 14:43:58 -0500, Jerry Avins <jya@ieee.org> wrote:
>>> AM is rarely used with digital modulation. It is primarily an analog
>>> medium.
>>
>> This maybe true for carrier based (and/or wireless) systems but for
>> base-band systems almost all modulation is AM. Best examples are 1GbE
>> (PAM5) and 10GbE (over 100m copper) which is 16 PAM.

There are lots more, like the 8-VSB used in the ATSC broadcast standard, 
OOK in most optical systems, etc., etc.

> I should clarify. By AM, I meant the system in which a carrier is varied
> in amplitude to create an envelope that follows the modulating signal,
> and can as a result be demodulated with an envelope detector. Variations
> that require taking phase into account lie outside the scope of my
> statement.
>
> Jerry

I knew what you meant, but also knew that it was ambiguous enough that 
people would point out QAM, etc.  The OOK used in optical systems is 
maybe the closest comparison for a digital modulation, but optical and 
RF power modulation systems are hardly comparable in that sense.

-- 
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com