[time-nuts] Performance verification for time counters

Poul-Henning Kamp phk at phk.freebsd.dk
Wed Nov 29 18:17:29 EST 2017

In message <5e3f68620fdb8f2e5d62e9907a44c6eb.squirrel at email.powweb.com>, "Chris Caudle" writes:
>On Wed, November 29, 2017 3:51 pm, Poul-Henning Kamp wrote:
>> While it is tempting and probably easiest to use a DDS style
>> generator, I recommend a synthesized one instead, to avoid
>> trouble with numeric spurs.
>Can you describe the distinction you are making between a synthesized
>generator, and a direct-digital synthesized generator?  I do not
>understand what would be meant by a synthesizer which is not DDS.

What used to be called a "Synthesized Signal Generator" was a almost
or even entirely analog beast, which means almost all distortion is
harmonic (2f, 3f, 4f, ...)

This is a good place to start, in particular the App-note at the


DDS is "Direct Digital Synthesis" where you basically generate the
desired signal with a computer and  D/A converter.  Because this
discrete rather than continuous in time, there are all sorts of
"weird" distortion products, and aliasing artifacts.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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