tags: mus-407 delay delay-line

Pitch-Shifting/Harmonization

Pitch-shifting/harmonization can be achieved using [variable delay lines], because a dynamically changing delay time produces [pitch] variance.

In our [circular buffer]:

• W/R pointers move at different speeds in the same direction
• if R is faster than W, output pitch is higher than input
• if R is slower than W, output pitch is lower than input
• modulate the delay time with a [sawtooth wave] to simulate a constant increase/decrease in speed of R
  • polarity (upward/downward slope) affects direction of pitch shift
  • magnitude of slope affects affects interval/distance of pitch shift

Central problem: At different speeds, R and W will periodically "pass through" each other, where R is likely to encounter a [waveform] discontinuity (heard as a click)

Solution/Digital Implementation

To solve the discontinuity problem:

• create several R pointers spaced out along circular queue, all moving at the same speed
• use [amplitude modulation] on each R pointer
• modulate the [amplitude] of each R pointer's output by unipolar [sine]/[triangle] wave
• control initial [phase] of each [oscillator] so circular queue discontinuity aligns with zero crossing of modulator [signal]
• sum R pointer outputs together

Summed signals (dry + wet) can have phase reinforcement/cancellation issues, but usually makes for a decent real-time harmonizer.

• caused by lining up delay time [resonance] with certain [harmonic]s, boosting some while cancelling others through [wave interference] (constructive vs. destructive)