Rob Rothwell wrote:

> Here is essentially what I want to do, which gives a "smooth" 
> (stepped) progression from f1 to f2.  stepsPerSecond sort of controls 
> the "smoothness" of the progression.
>
>     f1 := 330.50.
>     f2 := 440.90.
>     f := f1.
>     t := 0.
>     sec := 15.

...
Here's a version with PitchEnvelope, which is really smooth and much 
less complicated:
    f1 := 330.50.
    f2 := 440.90.
    sec := 15.
    envelope := (PitchEnvelope
            points: (Array
                with: 0 @ 1
                with: sec*1000 @ ((f2*2 / f1) log / 2 log))
            loopStart: 2 loopEnd: 2)
            centerPitch: f1.
    (FMSound new setPitch: f1 dur: sec loudness: 0.5)
        addEnvelope: envelope;
        play

Note that due to the logarithmic pitch slope, the frequency at t=7.5 is 
381.73 and not 385.70.
You should really experiment with PitchEnvelope a little more (and 
VolumeEnvelope for fade-in/fade-out).
I'm certain that you can achieve your goals with it.
When adding more slope points to the envelope, always remember to set 
loopStart and loopEnd to the size of the points array, as you don't want 
to have a looping part.

Cheers,
Hans-Martin