10.6

723Logic Pro Instruments
Resynthesis
You can analyze the frequency components of a recorded sound and then resynthesize—
reconstruct—a representation of the sound using additive or spectral techniques. See
Additive synthesis and Spectral synthesis.
At a basic conceptual level, additive synthesis and spectral (modeling) synthesis are similar
in that both techniques can recreate complex sounds by adding together many simpler
signals. In practice, however, the two methods are very different. Additive resynthesis
attempts to understand the harmonic structure of an audio file and then recreates each
harmonic partial with a separate sine wave. Spectral resynthesis instead analyzes the
changing frequency spectrum of the signal and attempts to recreate these spectral
characteristics in the resynthesized signal.
An additive resynthesis system generates a series of sine waves, with appropriate pitches
and levels over time, for each harmonic. It does this by calculating the frequency and
amplitude of each harmonic in the overall frequency spectrum of the analyzed sound.
After the sound has been resynthesized in this fashion, you can adjust the frequency
and amplitude of any harmonic (sine wave). Theoretically, you could even restructure a
harmonic sound to make it inharmonic, for example.
In a spectral resynthesis system, the audible spectrum is split into a large number of
“spectral bins,” and the distribution of energy across these bins is analyzed. The sound is
recreated by filling each spectral bin with the required amount of signal, either using sine
waves or filtered noise, and the results are then summed.
The difference in approach means the two techniques are suited to different types of
sounds. Additive resynthesis excels at recreating single notes with a clear harmonic
structure. Spectral resynthesis is better suited for complex inharmonic sounds such as
drums, or polyphonic material containing chords rather than individual notes.
Alchemy can resynthesize sounds using additive or spectral methods. It can also perform
resynthesis using a combination of the two techniques, which is useful for sounds that
feature both a clear pitch component and a noisy component. Examples of such sounds are
the hammer strike of a piano and the string tone, or the breath noise of a flute and the flute
tone.
Phase distortion synthesis
Phase distortion synthesis creates different waveforms by modifying the phase angle of a
sine wave with a second modulator wave. In some respects, this is similar to FM synthesis.
The principal difference between the two approaches is that the two waveforms are
synchronized each cycle in phase distortion synthesis, resulting in the creation of more
harmonic overtones.
In essence, you can bend a sine wave until it becomes a sawtooth wave, a triangle wave, a
square wave, and so on. The synthesis engine beyond the waveform generators typically
follows a subtractive synthesizer design.
Phase distortion synthesis was commercially introduced in the 1984 Casio CZ series
synthesizers.
Several Logic Pro synthesizers allow you to reshape the source waveform, but you are not
restricted to sine waves as the raw material.