Env doc: explain polyphony, copyedit.

Env.md

@@ -5,7 +5,9 @@
 Env is a combination pitch detector and envelope follower. Given an input audio signal,
 Env tries to detect the loudness and musical pitch of a single tone in it.
 
-Env is based on the pitch detector and envelope follower in the Surge XT [TreeMonster](https://library.vcvrack.com/SurgeXTRack/SurgeXTFXTreeMonster) module. Thanks to [BaconPaul](https://github.com/baconpaul/) for ideas and encouragement in this project!
+Env is mostly based on the pitch detector and envelope follower in the Surge XT [TreeMonster](https://library.vcvrack.com/SurgeXTRack/SurgeXTFXTreeMonster) module. Both Env and TreeMonster "naively" measure pitch frequency based on time intervals when the filtered waveform's voltage passing through zero. In other words, both count samples between zero-crossings and smooth out the result over time. Env uses a different prefilter (Cytomic with FREQ / RES) than TreeMonster (LO CUT / HI CUT). But the THRESH and SPEED controls are lifted directly from TreeMonster.
+
+Thanks to [BaconPaul](https://github.com/baconpaul/) of Surge XT for the idea for, and support of, this project!
 
 ## Controls
 
@@ -15,9 +17,34 @@ From left to right, each control consists of a CV input port,
 a smaller attenuverter knob, and a larger control knob.
 
 * **THRESH**: The amplitude threshold of the input signal needed to trigger pitch detection. The range is −94 dB to 0 dB, with a default of −24 dB. Adjust as needed to report pitch for valid notes while rejecting any low-level noise while notes are not playing.
-* **SPEED**: How quickly to slew reported output pitches. Lower values result in more stable note detection, but with a trombone-like glide through note changes. Faster values track changes in notes more quickly, but is more susceptible to unwanted variations of pitch.
+* **SPEED**: How quickly to slew reported output pitches. Lower values result in more stable note detection, but with a trombone-like glide through note changes. Faster values track changes in notes more quickly, but are more susceptible to unwanted variations of pitch (which can sound like birds twittering).
 * **FREQ**: Adjusts the center frequency of a bandpass prefilter that helps narrow in on the intended pitch range of the notes being detected. This can help reject unwanted harmonics from the input audio.
-* **RES**: Adjusts the resonance of the prefilter. Higher resonance can help squeeze the passband closer to the expected range of notes in the input audio. Too high a value can cause erroneous detection of notes at or near the center frequency.
+* **RES**: Adjusts the resonance of the bandpass prefilter. Higher resonance can help squeeze the passband closer to the expected range of notes in the input audio. Too high a value can cause erroneous detection of notes at or near the center frequency.
+
+## Polyphony
+
+Env is fully polyphonic, meaning all 5 of its input ports (AUDIO and the 4 CV input ports) allow
+independent control of up to 16 channels in the ENV and V/OCT output ports.
+Each channel of output represents a completely independent combined pitch detector and envelope follower.
+
+Whichever of the 5 input ports has the highest number of channels (1..16) determines the
+number of channels in the two output ports ENV and V/OCT.
+Any of the remaining 4 input ports having fewer channels will "clone" their final channel's
+voltage across all the required output channels.
+
+For example, if a cable connected to AUDIO has 2 channels (stereo),
+and a cable connected to the FREQ CV input port has 1 channel,
+and there are no other input cables,
+then the outputs ENV and V/OCT will each have 2 channels.
+Because in this example the FREQ CV signal has only 1 channel, that one channel
+will be used to satisfy the second channel also.
+
+If instead you used a 2-channel FREQ CV input cable, each of the two output channels
+in the ENV and V/OCT ports would set their respective prefilters using the two CV voltages,
+one for each channel in the output.
+
+This system of polyphony treats all the 5 input ports equally, using the rules explained above. As another example, you can put in 1-channel (mono) AUDIO
+but perform up to 16 simultaneous pitch/env operations, all with different settings, so long as at least one of your CV input ports has a polyphonic cable attached to it.
 
 ## Audio Input
 
@@ -39,4 +66,4 @@ there will be one channel of output for each channel of input on the AUDIO port.
 
 ## Attenuverters
 
-Env supports [low-sensitivity attenuverters](LowSensitivityAttenuverterKnobs.md).
+Env supports [low-sensitivity mode](LowSensitivityAttenuverterKnobs.md) for all four attenuverter knobs.