Stretch tuning in ES2 in Logic Pro for Mac

The (coarse) Frequency knob of each oscillator enables you to tune oscillators 1, 2, and 3 in semitones or octaves. The (fine tune) Frequency parameter enables you to fine-tune each oscillator in cents (1/100 of a semitone). Precise detuning between oscillators can result in beats, or phasing, between the oscillator frequencies. The higher the played frequency/pitch, the faster the phasing beats. High notes, therefore, may seem to be somewhat out of tune in comparison with lower notes.

CBD (Constant Beat Detuning) can be used as a corrective tool to even out the beating between oscillators, or it can be used as a creative tool to emulate stretch tuning. The latter can be particularly important when you use an ES2 sound alongside an acoustic piano recording. This is because acoustic pianos are intentionally tuned “out-of-tune” (from equal temperament). This is known as stretch tuning, and results in the upper and lower keyboard ranges being slightly out of tune with the center octaves but harmonically “in-tune” with each other.

Detuned oscillators periodically beat against each other at a certain frequency. CBD sets the beating frequency between low and high notes or retains a constant beating frequency across the keyboard range. Choose a CBD value to detune the harmonics/beating of low note frequencies in a ratio proportionate to the fundamental tone of the upper note frequencies.

CBD offers five values: off, 25%, 50%, 75%, and 100%. If you choose 100%, the phasing beats are almost constant across the entire keyboard range. This value may, however, be too high, because the lower notes might be overly detuned at the point where the phasing of the higher notes feels right. Try lower CBD values in cases where the bass notes are a little too far out of tune with the upper keyboard range.

The reference pitch for CBD is C3 (middle C): its (de)tuning is constant, regardless of the chosen CBD value.