[time-nuts] fast switching quiet synthesizer

Jim Lux jimlux at earthlink.net
Wed Oct 8 09:30:56 EDT 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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