Looks good if I understand it. I'm a little unclear on a couple of things
though:
1. Order of operations is not 100% clear. Are we doing
parenthesis->multiplication(and division)->addition, or something else? I
usually just use a million parenthesis. ;)
2. X squared keeping the original sign is not (|x| + x). I'm just assuming
that (x^2) means x squared keeping original sign, and not... that other
thing.
On Mon, May 13, 2013 at 3:48 PM, Paul Giblock <[email protected]> wrote:
> For anyone interested, here is how I decided to resolve this for the
> lmms-lv2 port:
>
> All three envelopes (vol, cut, res) behave the same: attack controls how
> long the envelope takes to reach 100% value, where it says for the length
> of hold (or until the note is released). The sustain amount is now a
> percentage of the maximum value instead of (1-max) as in LMMS. Thus, decay
> is how long it takes to reach the sustain level. Finally, release is how
> long it takes for the envelope to reach zero from the current value --
> regardless of the current state of the envelope. This provides a continuous
> function, and is in-line with all the descriptions of an AHDSR envelope
> that I've read. Note, channel (instrument) volume is not a factor here,
> that is performed AFTER mixing all the instrument's notes together.
>
> The big mystery in LMMS is how this envelope level (assume the output is
> between 0 and 1) maps to instrument parameters. For this, we let amt be the
> modulation amount (between -1 and 1). lfo_volume is the value of the volume
> LFO (between -1 and 1). Also, I use (x^2) as a shorthand for (|x| + x),
> that is: x squared, while maintaining the original sign.
>
> envelope_volume = envelope_level * amt + (1-amt), if amt >= 0
> envelope_volume = envelope_level * amt + 1, otherwise
>
> volume = (envelope_volume * lfo_volume)^2, if lfo_modulate_env
> volume = (envelope_volume + lfo_volume)^2, otherwise
>
> LMMS, thus maps the envelope value to a velocity quadratically instead of
> linear or exponentially. Perhaps due to the perceived volume difference?
> Also, the volume envelope "Amount" knob is the ratio of enveloped to
> non-enveloped signal -- not the maximum volume. This seems fine to me,
> although I might adjust the quadratic mapping to something more musical
> such as dB? The cutoff and resonance envelopes do not perform the same
> "mixing" operation. Thus, the amt value is actually the magnitude of the
> envelope:
>
> envelope_cut = envelope_level * amt
>
> cut = knob_cut + (envelope_cut * lfo_cut)^2 * 6000.0, if lfo_modulate_env
> cut = knob_cut + (envelope_cut + lfo_cut)^2 * 6000.0, otherwise
>
> The resonance envelope and LFO behave the same as the cutoff, but is
> scaled to 2.0 instead of 6000.0. I personally feel this whole system is
> adequate and fairly straight-forward. However, I will try to replace as
> many of these magic [0..1] or [-1..1] parameters with proper values and
> units. Seconds for attack, hold, decay, release. Percentage for sustain.
> Perhaps dB for volume amount and Hz for cutoff -- although that may not be
> possible due to the dynamic nature of those two knobs.
>
> -- Paul
>
>
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--
Johnny
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