Sound

Digital Delay For Application in Surround Sound

7.0 Further Work

7.1 DIGITAL

DIGITAL SIGNAL PROCESSING

Digital Signal Processors (DSP's) are becoming more common place in the processing of audio signals. The use of a DSP to base the delay and analogue processes on would have a number of advantages:

Firstly the difference and summation processes could be carried out in the digital domain ensuring greater flexibility and control.

The delay time constant criterion could then be altered more easily than its dedicated hardware counterpart, i.e. instead of having a minimum of 1 ms time delay, it would be possible to reduce this to a smaller (or larger) value if and when required.

The system could be made even more flexible if the original signal could be taken in directly from a digital source, such as the digital output available now on most CD players (SPDIF, etc). The processed signal could then be made available in a similar digital form for interfacing directly with other digital equipment, such as digitally controlled loudspeakers, etc, as well as catering for an analogue out.

OVERSAMPLING

The characteristics of the reconstruction filter after the DAC cause severe phase distortions to the output signal, particularly at the higher frequencies. By the use of oversampling, a filter with a much lower order could be used, thus preserving the phase characteristics of the original signal more.

7.2 GENERAL

DECODERS

As a result of background reading on surround sound, the subject of ambisonics appeared to be an interesting area in which it may be possible to carry out more work.
It would be feasible to construct a fully working ambisonic decoder and a Dolby surround decoder, as well as circuitry to derive sub-bass information, and incorporate it all into the existing design.

ENCODERS

It would also be interesting to work in the field of surround sound encoders, particularly for Dolby systems and that of ambisonics, with the aim of creating systems that are aimed more at the music side, as opposed to the film side, particular for popular and electronic music.

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