[time-nuts] fast switching quiet synthesizer
jimlux at earthlink.net
Wed Oct 8 13:30:56 UTC 2014
On 10/8/14, 12:52 AM, Hal Murray wrote:
> bruce at ko4bb.com said:
>> Kratos (www.kratosepd.com) do fast switching synthesiser subsystems that
>> can be locked to a reference..
> What does "fast switching" mean in the context of a DDS?
How long does it take to load the new phase increment in?
I suppose one can distinguish between "load" and "set/settle" time, and
for a DDS the latter is "one clock".
(although for DDSes that include post NCO filtering for spur
reduction/movement, there might be a longer transient, depending on the
kind of filter)
> What does the spectrum of a DDS look like if I switch back and forth between
> 2 frequencies at 1 KHz? Or what question should I be asking?
It would look like a phase continuous FSK signal. If you switch fast
(e.g. at rates comparable to the shift), then the spectrum gets quite
(this was basically the basis of the Yamaha FM synthesis approach for
music synthesizers.. it produces a very rich spectrum with lots of
overtones and intermod products and can produce very natural sounding notes)
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