asleep at the wheel..

[SYSph@ntOPus]

I figured as much. Ain't technology grand?

On Thu, 28 Oct 1999, Batz Goodfortune wrote:

> Y-ellow SYSph:
> 
> At 12:36 PM 10/27/99 -0500, SYSph at ntOPus wrote:
> >Could someone define a free running LFO for me just to make sure I'm on
> >the same page as everyone else? Sorry about the lack of attention...
> 
> The term "Free running LFO" I guess is rather like "Sysex on the fly". Both
> terms would never have come about other than for modern technology which
> seeks to cut corners.
> 
> A free running LFO is like that on a modular. You simply select a speed and
> send it to something. It is not restarted or effected by a key-on event or
> any other event for that matter. It just keeps on pumping out very low
> frequency wave forms.
> 
> It's one way of doing filter sweeps for example. A great many synths (way
> too many) because  of their corner cutting nature -as mentioned in a
> previous post about LFOs in poly synths- will restart the LFO on every
> key-on event. Subsequently even if your LFO is running @ 0.01Hz, it will
> behave more like an envelope than an LFO unless the key is held constantly.
> Which means you can't do filter sweeps or even rippling timbres across a
> sequence of events. Only during the transient of a single note. Does that
> make sense to  you?
> 
> Some older mono synths had the curious feature of allowing an LFO delay.
> The effect of the LFO would not be active upon the voice for a time period
> set by the delay. After which the effects would either A) turn on suddenly
> in the  case of a cheap-assed synth or B) slowly increase in magnitude in
> the case of a properly designed synth. It is reasonable  to assume that you
> could also have a setting which would allow you to delay the LFO then set
> the time interval over which it would increase it's effect. I've never seen
> such an LFO but it's possible. 
> 
> In a cheap synth  the delay setting and the LFO are intrinsically linked
> such as the LFO will always Come on or re-trigger at the key-on instant and
> increase in effectiveness over time. A better designed synth will allow the
>  LFO to free-run when the delay  is set to zero. Such that the LFO is not
> effected by an external event unless otherwise programed to do so. If you
> wanted the LFO to be triggered by the Keyboard or what ever, but you wanted
> it to be reasonably instantaneous,  you'd simply raise the LFO delay ever
> so slightly. Otherwise it would free run.
> 
> Alas cheap-assed modern digital synths based on single chip sample playback
> engines, such as those found on $10 sound cards and 9000 dollar samplers
> (they're all pretty much the same) generally don't offer free running
> synths for technical reasons. Even some well known CPU controlled analogue
> synths have this deficiency and it's all to do with dynamic assignment. And
> you can Thank Roland for that...
> 
> As previously mentioned, Dynamic assignment has the advantage of giving you
> more apparent voices than you actually have. You might have a 16 voice
> polytimbral synth. Pumping each channel theoretically allows you to play 16
> notes at once on all 16 channels giving a theoretical number of voices of
> 256 voices. Just as long as you don't play more than 16 of them at any 1 time.
> 
> The way these things work is that they have 16 generic voice channels. The
> actual voice parameters are assigned to which ever voice is free at any
> given time. So while a given voice channel might be a poly pad one second,
> it could be a kick drum the next. This means that every time a new note is
> assigned to a voice channel, a new LFO is defined for that voice channel as
> well. It cannot, by definition, be "Free-running".
> 
> As mentioned before, as a designer you can do one of 2 things. You can
> capture the phase and rate of the LFO and re-instate it over time on the
> next iteration of that voice. Or you can simply have 1 or more external
> free running LFOs. The former is better because it allows you to have a
> free running LFO on every voice, but as you can imagine, it adds a
> magnitude of complexity to the system. Alright for your DSP heads with a
> little CPU bandwidth to spare but technically difficult in hardware. Unless
> you're designing a custom chip or 3.
> 
> Yamaha never had this problem because for years they refused to follow
> Roland's lead and kept with their policy of pre-defined polytimbrality.
> Since each voice and it's associated level of Polyphony had to be
> pre-defined in advance, all 8 or 16 LFOs per voice could be allocated in
> advance and therefore you could elect to have a free running LFO on every
> voice if you wished. Later, when Yamaha succumbed to the dark side, they
> instantly found that continuing this tradition was not easy. So naturally
> they dropped it.
> 
> Which is a damn shame. Synths like the little TG55 would be ace wicked if
> it weren't for that. It has kick-ass filters but you can't do a filter
> sweep because it's LFO won't free run. And due to a slight misjudgment in
> it's software, you can't actually sweep the filter from MIDI once the key
> is pressed. It simply locks out the controller until another key is
> pressed. This can actually be quite useful some times but if you're trying
> to "WOW" a voice by hand to give it some formant (read vocal) qualities,
> forget it. It can't be done.
> 
> And just to sum up. As I said in the beginning, This terminology would
> never have come into usage if we had all stuck with modular synths. Since
> you define the LFO's parameters and it free runs of it's own accord. It was
> just a given that it worked like that. I don't recall any modular synth
> I've ever used even having the ability to re-trigger the wave form. Why
> would you want to? The only reason they do it now is due to the technology
> of dynamic assignment they use. And, in the words of Monty Python. "It
> get's me very irritated!"
> 
> be absolutely Icebox.
> 
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