SSB

[mark verbos]

Gene Stopp wrote:

> Yes! There does exist such a device for musical applications - called a
> "Frequency Shifter", and produced in the past by 360 Systems (can be heard
> on John McLaughlin albums), by Moog (called the "Bode Frequency Shifter",
> and heard on some Tomita albums), by Serge, and as a project in
> Electronotes. There may be others out there, but these I know of.
> 
> Technically a Frequency Shifter is a single sideband modulator, as opposed
> to a double sideband modulator which is the technician's name for a ring
> modulator (or "balanced modulator", or even a "mixer" in some radio
> circles). The circuit consists of a pair of 90 degree phase splitters, two
> ring modulators, and an output mixer. The 90 degree phase splitters can
> consist of either a quadrature sine wave source, or a live signal wideband
> phase difference network. You can make a frequency shifter with both 90
> degree splitter sources as quadrature oscillators, but this is really just
> an expensive way to create sine waves. You can make one with two live
> signal 90 degree phase difference networks, which would produce results
> that may be a bit too complex for easy operation (and besides, expensive
> since the 90 degree PDN's are quite parts-intensive). The most typical
> application involves a quadrature sine wave source plus a live signal 90
> degree PDN.
> 
> The Electronotes circuit (which is included in the Preferred Circuits
> Collection BTW) has a fairly easy-to-build 90 degree live signal PDN which
> covers the audio range and consists of only a few op-amps plus some
> carefully selected parts. The quadrature since wave VCO is of the beat
> frequency type which allows through-zero FM - it creates a sin and cosin
> output by mixing a fixed 20 KHz sin/cos pair with a 15 KHz-25 KHz VCO sine
> wave with two ring modulators. This method tends to drift a bit since
> keeping a 20 KHz VCO to within a single cycle over time is not easy.
> However, with this method the FM capabilites are maximized. The circuit is
> more complex than most projects (including a total of four ring
> modulators!) and is probably not for the beginner, but it is quite
> satisfying for those who like to build.
> 
> Sound-wise, the highly technical designer of the circuit (the famous Bernie
> Hutchins) refers to the effect as "dramatic", which in Electronotes
> terminology means "pretty darn weird sounding". I've built this module and
> it's true - the sound can be pretty out there. Basically the transformation
> of a live signal (any sound source, such as an instrument or human voice)
> will be warped so drastically as to be almost unrecognizeable, for large
> modulation amounts. Major inharmonic stuff going on here, but not quite the
> same as a ring modulator. I suppose I would call the output "less confused"
> compared to a ring modulator, meaning that you can hear the shift effect
> more clearly than with a ring modulator since there are only sidebands on
> one side of the signal (either above or below the signal being modulated,
> depending on the direction of modulation).
> 
> A rather obscure example of the effect on a human voice can be found in the
> alien being vocal effects in some episodes of the old TV show "The Outer
> Limits" (one such episode would be the pilot show, entitled "The Galaxy
> Being").
> 
> All in all I think that it's worth the effort of either building one or
> finding a used one. I suspect that the Electronotes version may be the
> cleanest of all, due to the use of Analog Devices balanced modulator chips
> plus a pair of noise gate VCA's on the output driven by a precision
> envelope follower (jeeez I'm realizing just how good that circuit really
> is!). A bit expensive (the chips cost me about $120 total, just for the AD
> parts) but worth it.
> 

anybody have one of these schematics handy (or all of them;)? I don't have the electronotes 
and would love to see these designs. I used a frequency shifter someone DIYed and it blew me 
away, he claimed it was a custom design, but it was probably electronotes'.

Mark