User guide

Tracktion 4 Reference Manual
8
CD audio has a resolution of 16-bits. Modern sound-cards and audio devices can record at 24-bits or
higher. A big advantage of recording at these higher bit depths is that you can reduce your input level
enough to ensure that digital clipping is very unlikely to occur, while still maintaining a resolution that is
greater than CD. Lowering the level may also help to reduce noise levels.
Sample Frequency (Sample Rate)
It is all very well having an accurate recording device, but recordings also need to be made fre-
quently enough to be meaningful. If you were to take the temperature outside of your home, you would
expect to obtain different results at different times of the day. If you were to look at your thermometer
only at midday though, you only ever see one temperature, and you could be forgiven for thinking that
it pretty much stays constant all day long. This is because your sampling frequency matches the fre-
quency of the temperature cycle. To get a more accurate idea of how temperature changes throughout
the day, you’d need to at least double the frequency of measurements, and take a second reading at
midnight. In sampling terms, the need to record at a frequency at least double the highest desired fre-
quency is known as Nyquist’s Theorem. It is also the reason why CDs are recorded at 44 kHz, when
the human ear can only hear up to around 22 kHz.
The sample frequency, therefore, is quite literally the number of times per second that the amplitude
of an audio signal is measured.
When choosing a sample rate to record and work at, it is usually best to simply opt for whatever fre-
quency at which your work will be distributed. If, for example, you are making music, and intend to have
it printed to CD, you should probably work at 44.1 kHz.
Tip: If you wish to work at higher frequencies, and render down to a lower frequency when your proj-
ect is complete, it is probably best to work at direct multiples of your target sample rate, e.g., 44.1 kHz
and 88.2 kHz.