func mixLogarithmicRangeCompression(i sample.Value) sample.Value {
if i < -1 {
return sample.Value(-math.Log(-float64(i)-0.85)/14 - 0.75)
} else if i > 1 {
return sample.Value(math.Log(float64(i)-0.85)/14 + 0.75)
} else {
return sample.Value(i / 1.61803398875)
}
}
// volume (0 to 1), and pan (-1 to +1)
// TODO: ensure implicit panning of source channels! e.g. 2 channels is full left, full right.
func volume(channel float64, volume float64, pan float64) sample.Value {
if pan == 0 {
return sample.Value(volume)
} else if pan < 0 {
return sample.Value(math.Max(0, 1+pan*channel/masterChannelsFloat))
} else { // pan > 0
return sample.Value(math.Max(0, 1-pan*channel/masterChannelsFloat))
}
}
func TestMixer_mixVolume(t *testing.T) {
masterChannelsFloat = 1
assert.Equal(t, sample.Value(0), volume(0, 0, 0))
assert.Equal(t, sample.Value(1), volume(0, 1, .5))
masterChannelsFloat = 2
assert.Equal(t, sample.Value(1), volume(0, 1, -.5))
assert.Equal(t, sample.Value(.75), volume(1, 1, .5))
assert.Equal(t, sample.Value(.5), volume(0, .5, 0))
assert.Equal(t, sample.Value(.5), volume(1, .5, 1))
masterChannelsFloat = 3
assert.Equal(t, sample.Value(1), volume(0, 1, 0))
assert.Equal(t, sample.Value(0.6666666666666667), volume(1, 1, -1))
assert.Equal(t, sample.Value(0.6666666666666667), volume(2, .5, -.5))
assert.Equal(t, sample.Value(0.6666666666666667), volume(1, .5, 1))
masterChannelsFloat = 4
assert.Equal(t, sample.Value(1), volume(0, 1, -1))
assert.Equal(t, sample.Value(1), volume(1, 1, 0))
assert.Equal(t, sample.Value(.75), volume(2, .5, .5))
assert.Equal(t, sample.Value(.625), volume(3, .5, -.5))
}