Apple Soundtrack Pro 3 - Manual (Page 489)

Phase cancelation can be a problem when mixing similar audio signals together, or when
original and reflected sound waves interact in a reflective room. For example, when the
left and right channels of a stereo mix are combined to create a mono mix, the signals
may suffer from phase cancelation.
In phase
Separate signals
Mixed signals
Out of phase
Frequency Spectrum of Sounds
With the exception of pure sine waves, sounds are made up of many different frequency
components vibrating at the same time. The particular characteristics of a sound are the
result of the unique combination of frequencies it contains.
Sounds contain energy in different frequency ranges, or bands. If a sound has a lot of
low-frequency energy, it has a lot of bass. The 250–4000 Hz frequency band, where humans
hear best, is described as midrange. High-frequency energy beyond the midrange is called
treble, and this adds crispness or brilliance to a sound. The graph below shows how the
sounds of different musical instruments fall within particular frequency bands.
Time
Bass
M
id
High
Cymbal crash
20 Hz
300 Hz
4 kHz
20 kHz
Violin and flute
Cello
Bass line
Fr
equenc
y
489 Appendix B Audio Fundamentals