Anthony Walter via lazarus wrote:
Marc,
That is interesting and you've given me something to consider and
perhaps adjust. Thank you.
Also with regards to attack and release, I've opted to call it just
attack. That is when the note is starting to play, or ending playing, I
perform a short fade of the wave form on both ends using the same value.
I also mix in a sustain which I am using to fade the note out over time
after the initial attack.
So the formula I am using is assuming a note is playing (StartTime >=
CurrentTime):
if StartTime - CurrentTime < Attack then
Mix := StartTime - CurrentTime / Attack
else
Mix := 1;
Then I used the Mix blend variable to adjust the wave amplitude (Volume)
by multiplying it against the left and right channels.
// Sample Left and Right are a 16 bit signed integers
Sample.Left := Trunc(AudioWave(F) * Volume * Mix);
Sample.Right := -Sample.Left;
Where:
F is the a value between 0.0..1.0 representing the current wave cycle
AudioWave is the user defined function to convert F into a wave shape
returning a value between -1.0..1.0
Volume is the peak we allow for the Left or Right on Sample (in my case
the constant value 2048)
Mix is between 0.0..1.0 and is used to fade in for attack, fade out for
release, and fade out using sustain
So I should fix this by adding a tiny bit of phase change to F based on
which keyboard key is being processed.
As long as you don't reset F to 0 when playing a new note this should work.
To verify, you can use Audacity to record the generated audio (or write
it to file as raw pcm). If you switch to spectogram view, you see those
phase errors as a spike in the diagram
Marc
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