10.6

719Logic Pro Instruments
Sample-based synthesis
Sample-based synthesis, which is sometimes known as Pulse Code Modulation (PCM), or
sampling and synthesis (S&S) synthesis, is differentiated from subtractive synthesis mainly
by the use of samples in place of oscillator waveforms.
The samples—digital recordings of existing sounds—are mapped across the keyboard.
Typically, each sample is mapped to a note in the center of a keyboard range that spans a
few notes that are unique to that sample. The reason for this limited range of notes is that
samples tend to sound much less like the source sound if played more than a few notes
higher or lower than the original pitch—due to the relationship between the pitch and
playback speed of samples.
The pitch of each sample isn’t changed with a frequency control, unlike the oscillator
waveform of a synthesizer. Rather, a sample is played back at a faster or slower speed
to alter its pitch, which has a corresponding impact on the sample playback time. For
example, a sample played back at twice the speed requires half the time to play through.
Sampler is a sample player that can be used much like a sample-based synthesizer, due
to the subtractive synthesis features that it offers. Alchemy can also be used in this way,
but adds additive and spectral resynthesis features that can result in very different sounds
than are possible with subtractive synthesis techniques. Alchemy also provides a granular
synthesis engine that offers further sample manipulation options, again extending the
potential sonic outcome. See Resynthesis and Granular synthesis.
Popular instruments that use the sample-based synthesis approach include the Korg M1,
O1/W, and Triton; the Roland JV/XP instruments; the Yamaha Motif series; and many others.
Frequency modulation (FM) synthesis
FMsynthesis uses a modulator oscillator and a sine wave carrier oscillator. The modulator
oscillator modulates the frequency of the waveform generated by the carrier oscillator
within the audio range, thus producing new harmonics. These harmonics are known as
sidebands.
Where there is a mathematical relationship between the carrier and modulator waveforms,
the sound produced is harmonic. Where the modulator is a non-integer multiple of the
carrier waveform, inharmonic sidebands are produced, resulting in an inharmonic sound.