[sdiy] VSM201 Vocorder Question

[Chris Juried]

Yes. Very good point, Richie.
 Sincerely,   
  Chris Juried  
Audio Engineering Society (AES) Member  
InfoComm-Recognized AV Technologist
http://www.JuriedEngineering.com (Juried Engineering, LLC.)
http://www.TubeEquipment.com (Tube Equipment Corporation)
http://www.HistoryOfRecording.com (History of Recording)

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      From: Richie Burnett <rburnett at richieburnett.co.uk>
 To: Tom Wiltshire <tom at electricdruid.net> 
Cc: synth-diy at dropmix.xs4all.nl
 Sent: Saturday, January 2, 2016 4:12 PM
 Subject: Re: [sdiy] VSM201 Vocorder Question
   
With carrier frequency of 50kHz, 0.01% duty ratio (for 80dB attenuation) represents a pulse width of just 2ns! That's getting near the sort of time mismatch you can get in turn-on and turn-off times for the switches. So the switch might not turn on at all, or might stay on twice as long!

-Richie,

Sent from my Xperia SP on O2

---- Tom Wiltshire wrote ----

>+1 totally agree
>
>If you can produce a 1% pulse width, you still only get -40dB. You need to get a 0.01% pulse wave to get -80dB. Tough to do. Not impossible, but awkward enough to make it stop seeming like such a great solution.
>
>I've thought about this a bit because of using the PIC's PWM module so much. The best case output from that is either 8-bit or 10-bit, which means that -60dB is about as good as I'd get using it for a VCA, and that implies having a switching frequency which is much too low (31KHz) for many jobs.
>
>Tom
>
>
>On 2 Jan 2016, at 19:42, rburnett at richieburnett.co.uk wrote:
>
>> <snip>
>> Control range of PWM'd CMOS switches acting as VCAs isn't that great though.
>> 
>> -Richie,
>> 
>
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