User guide

Tracktion 4 Reference Manual
7
Sample Resolution (Bit Depth)
Although perhaps a strange analogy, a thermometer is a good model for describing sample resolu-
tion. Imagine that you have a thermometer which is graded from the freezing point of water through
to its boiling point. The accuracy with which you can measure the temperature of a cup of tea would
be dependent on how many marks there are on the scale. A thermometer whose scale jumps in incre-
ments of 10 degrees would clearly be less accurate than a thermometer offering a scale in terms of
single degrees.
So, how does this tie in to digital audio? Well, reading a thermometer is largely a digital process. That
is to say, while there is theoretically an innite spread of possible temperatures between freezing and
boiling, if you were to record them, you’d be using nite approximations. The temperature may be 50.2
degrees, but you would write down 50 degrees. This is exactly what happens with digital audio. The
number of tick marks shown between the minimum and maximum temperature can be thought of as the
sampling resolution.
Figure I.2.2
shows what happens to a sine wave when the amplitude is measured. The rst image
shows the sine wave when only two states are possible, either on or off. The second image shows the
same sine wave reproduced with slightly less coarse graduations. Finally, the third image shows how
increasing the sampling resolution produces a greatly more accurate impression of the original sine
wave. So, when people talk about bit-depth, or sample resolution, what they are in effect describing is
how accurately an audio signal’s amplitude can be measured.
Getting back to that thermometer for a second, what happens if the temperature being measured
exceeds the boiling point of water? Well, in short, the temperature cannot be accurately recorded, and
you would have to log it as “off the scale.” If, for example, you were to heat a beaker of water to just
above boiling, then allow it to cool, a chart showing temperature over time might look something like
Figure I.2.3.
Because the thermometer cannot measure temperatures above boiling, a whole section of the chart
has been cut off (or clipped). Exactly the same thing happens when audio is being recorded digitally.
Any audio that exceeds the maximum recordable level is simply clipped which produces a very unmusi-
cal form of distortion.
Figure I.2.2
Figure I.2.3