Digital Music Composition/Sound in the time domain

Sound In The Time Domain

Acoustically, sound is a variance in air pressure which is picked up by the human hearing system and converted into electrical impulses via transduction. These signals are analysed by the brain and presented as audio information. Similarly, audio information in the digital domain is represented by a sequence of numbers (samples) which represents amplitude as a function of time, and as such describe the fluctuations in air pressure that sound creates.

Fig. 1. Image of a waveform or suitable graphic

Fig. 1 shows the most common way that audio is viewed on computers. This time-domain method displays each sample value in time, creating visual data which helps the user to see, primarily, the amplitude of the sound; this process benefits the editing and sequencing of audio in many cases. On the other hand, it typically does not reveal much about the timbre or sound color of the incoming audio, which is better represented by a spectrogram.

Fig. 2. Image of sound analysed using a spectrograph

The spectrogram shows us frequency as a function of time and is typically referred to as a frequency-domain method of analysis (however, strictly speaking, the 'domain' is still time). We can discern far more about the timbral quality of the sound due to the fact that each individual frequency can be represented on the graph. An example of an application of this technique might be to understand the frequency content of a sound for synthesis; particularly techniques such as additive resynthesis. The processing power required to produce a spectrogram is much greater than a time-domain analysis due to the greater complexity of the underlying algorithms.