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Digital Audio Investigation Introduction: This investigation will study the principles and stages behind A/D and D/A conversions, it will also state the different problems encountered in digital audio, and resolve them by deciphering the key issues. As part of the investigation a practical demonstration will be devised in order to understand the relation between bit rate and levels of definition within the processed signal. Part 1: Analogue to digital converters The first step in digitalising an analogue waveform is to change an occurrence that happens in ‘continuous time’ into one that is chopped into slices of ‘discrete time’. This principle is used when filming, for example when someone watches a film they see a smooth motion, but in actual fact they only see 24 photos (frames) per second. (See figure 1) Figure 1 The problem with chopping continuous time into slices of descrete time is that distortion can occur if the slices aren’t small enough, this is known as Aliasing. The result of aliasing can cause two problems, the first is that frequencies above half the sample rate (Nyquist frequency) may get into the sample and hold circuit, and the second is that a low sample rate will not