Reference Guide

756
Editing audio
Digital audio fundamentals
The decibel scale
In acoustics, the decibel (dB) scale is a scale for measuring the relative loudness of two sounds. For
example, environmental noise is often measured as follows:
L = 20 log (p/p0)
where L is the sound pressure level (in dB), p is the sound pressure amplitude, and p0 is a reference
amplitude of 20 micropascals (less than one billionth of atmospheric pressure). On this scale, a
barely audible sound (p = p0) has a sound pressure level of 0 dB, normal conversation (p =
1,000*p0) is at a level of around 60 dB, and a jet engine at close range (p = 1,000,000*p0) is at a
level of around 120 dB.
Similar decibel scales are used in other branches of science and engineering to measure electrical
power levels and other signal levels, always with respect to some reference level.
In SONAR, decibels are used in several places:
• To indicate volume levels of audio tracks in the Track view, Track Inspector and Console view
• To indicate the effects of filters and equalizers
The reference level (0 dB) usually corresponds to the current loudness of the sound. A positive
change in decibels makes the sound louder; a negative change makes the sound quieter.
See:
“Digital audio fundamentals” on page 750
Audio clips
If you have read “Digital audio fundamentals” on page 750, you should have a good idea of what is
contained in a SONAR audio clip. An audio clip contains a long series of numbers, or samples,
representing the fluctuating amplitude of a waveform. Audio clips are typically quite large, hundreds
of kilobytes to many megabytes in size. By comparison, a MIDI event takes only a few bytes to store.
The Track view lets you see your audio waveforms in great detail; you can zoom in until you see the
individual samples.
You should also now be aware of some things to watch out for when editing your audio data. First, if
you cut audio clips apart or splice them together, you should do so at zero-crossings in the
waveform (places where the amplitude is zero), in order to avoid sudden changes in amplitude that
may cause clicks and pops. Second, you should beware of clipping. Clipping of the audio waveform
can occur if you record a signal at too high a record level, or if you apply audio processing or effects
that increase the waveform amplitude too much. If you accidentally cause the waveform to clip, you
should undo the command and try again with different parameters.
Clipping can also occur in other situations, for example, if you try to play or mix several loud audio
tracks together, the aggregate signal strength may at times exceed the clipping limit, and the output
signal will be distorted. To correct the problem, you can create a volume envelope to reduce the
level in loud audio clips or reduce the track volume in the Console or Track views.
See:
“Digital audio fundamentals” on page 750