Some of asked for this:
ENVELOPES IN THE C4
8/19/19
The Source Audio C4 Synth pedal has two envelope followers available. They both have the same capabilities, but their control parameters may be set differently. Input 1 or input 2 may serve as the input signal to either. An envelope follower uses its audio input signal to output a representation of how loud the audio is at the moment. Louder signals get a higher output level from the envelope follower.
Since the audio signal goes both positive and negative, we first take the absolute value of the audio; negative values are replaced by the same number, but made positive. A certain amount of smoothing is necessary, because the input signal will repeatedly go to zero, but at a rate which we don't perceive as a level change, since it is happening too fast for us to hear like that. Deliberately introducing a slower than necessary smoothing will cause the output to move more slowly than the actual audio signal changes. Different smoothing rates for attack (a rising output) and decay (a falling output) permit more control over the final response.
Whereas a typical synthesizer has a controllable release time on its envelopes (which begins when one takes their hand off a keyboard note), we have the problem that the guitar sound is over when a note is through. A synthesizer oscillator would still be running, but the pitch detector output tends to lose it as a note is dying away, so the synth oscillator is also not reliably available after note end. So our final release times are always quite short.
We also offer ADSR type envelopes (attack – decay – sustain – release). The attack segment begins when an attack threshold level is exceeded. When the envelope level gets to 1.0 (full scale ON), the decay segment takes over, dropping until the sustain level is reached. When the input gets below a release threshold, we go into a (fast, as always) release segment. These threshold levels are fixed. One more reason to do the Input Gain Calibration procedure, to make sure your guitar signal is in the proper range, for the fixed thresholds.
All of these possible envelope controls are not brought out to the user interface. This is partly due to trying to save bits in the preset data (and if you had asked me 50 years ago whether saving bits would still be a thing in 2019, I would have laughed), and also to keep the complexity down. Reasonable people may disagree that boiling down a lot of controls into only a few, with a selection of envelope types, is really simpler. But that's the way it is.
The Envelope Type definitions:
Atk_lo Atk_hi Dec_lo Dec_hi Fast_atk ADSR Sustain
0 ADSR Adj A/D 0.2 1.0 0.2 0.6 N/A YES 0.0
Both A and D are controlled by the Speed control. With Speed = 0 (full counterclockwise), we use an Attack control value of 0.2. When Speed = 1.0 (full clockwise), the Attack control is 1.0.
1 Fast A, Adj D 0.7 0.7 0.2 0.85 0.05 NO N/A
The Attack control is fixed at 0.7.
2 Wide 1, Adj A/D 0.0 1.0 0.2 0.6 0.03 NO N/A
3 Swell 0.0 0.4 0.0 0.2 0.02 NO N/A
Slowest attack.
4 Wide 2, Adj A/D 0.0 1.0 0.5 0.8 0.07 NO N/A
Same Attack range, but Decay is faster than #2.
5 Snappy 0.6 1.0 0.4 0.75 0.15 NO N/A
Fast.
6 ADSR Fast A, Adj D 0.9 1.0 0.1 0.55 N/A YES 0.0
7 ADSR Adj A/D 0.0 1.0 0.2 0.5 N/A YES 0.0
8 ADSR 4 0.9 1.0 0.1 0.55 N/A YES 0.2
Same as #6, but with a Sustain level of .2.
9 ADSR 5 0.0 1.0 0.2 0.5 N/A YES 0.2
Same as #7, but with a Sustain level of .2.
10 ADSR Slow A, Fast D 0.0 0.5 0.55 0.55 N/A YES 0.0
13 Fastest A, Adj D 1.0 1.0 0.2 0.8 0.5 NO N/A
The Speed control goes from 0.0 to 1.0, for both Attack and Decay times. This is translated to the following range of what are called "time constants". (After one time constant, a decaying signal has dropped to 36.8% (or -8.7 dB) from its starting value.)
Speed Time Constant
1.0 .65 msec
0.75 6.5 msec
0.5 65 msec
0.25 650 msec
0.0 6.5 sec
The Fast-Attack number controls exactly how fast the initial attack can rise. 1.0 is instantaneous; 0.5 is the fastest used. Most are considerably slower. The ADSR envelopes do not use this control.
Sustain is the ADSR sustain level. Most are 0.0, with two at 0.2.
can’t wait to mess with it and try out the community presets.
