Sound

Digital Delay For Application in Surround Sound

3.0 DESCRIPTION OF PRACTICAL WORK

All circuits were constructed on veroboard and the processor comprises of seven separate circuit boards in total.

Each of the seven circuit boards dealt with specific parts of the signal processing.

3.1 CONSTRUCTION DETAILS

Construction of one single circuit board was a four stage process once the overall circuit had been designed:

1) An overall block diagram of the circuit was drawn up on paper, roughly outlining the interconnections between sections.
2) A chip pin-out drawing was made, showing all connections between I.C.s and also included connections to power rails. NOTE: all I.C. power rails were decoupled to ground with a capacitor as close to the I.C. as possible.
3) A dot-to-dot diagram was made. This consisted of a piece of paper with dots regularly spaced at 2.5mm intervals representing the holes on the veroboard copper tracks. Information such as placings for I.C. sockets, components, tinned copper wire links, vero pins and standard wire links could be conveyed and also which tracks needed to be cut.
4) The final stage was the physical construction of the circuit by referring to the dot-to-dot diagram.

3.2 CIRCUIT BOARD DETAILS

3.2.1 14-Bit Up Counter Board

This contained the four cascaded 4-bit counters configured in UP mode, (refer to section 2.1.1). The fourteen bit word was terminated on both edges of the circuit board.

3.2.2 RAM Board

This contained the two UPD43256A chips, (refer to section 2.1.1).

3.2.3 Conversion Board

This dealt with the overall conversion processes and contained the ADC, DAC, latches and inverters (refer to sections 2.1.1).

3.2.4 Control Board

This routed the signal from the MASTER RESET line to the correct places. It also took the information from the incremental encoder for the 8-bit up/down counter and issued a reset pulse to the 14-bit up counter from the 8-bit comparator for the time delay control.
The control board also contained the display driver I.C. (refer to section 2.1.2).

3.2.5 Clocks and Master Reset Board

This board was responsible for generating all the appropriate timing signals and for issuing the initial master reset pulse (refer to section 2.1.3).

3.2.6 Analogue Board

The analogue board consisted of both the input and output stages, (refer to sections 2.2.1 and 2.2.2).

3.2.7 Power Supply Board

A single veroboard was used for the power supply, although the toroidal transformer was not mounted directly on the board, instead being mounted to the case, (refer to section 2.2.3).

From FIG 3.0, the layout of the boards can be seen more clearly.
Different circuits types are isolated from each other by metal dividers. i.e. the power, analogue and digital circuits are separated.
In the top left corner is the power board and transformer. In the top right corner the analogue board.
Below in the bottom right corner is the control board, with the conversion board mounted directly underneath it. In the Bottom left corner is a stack of three boards; the clocks and master reset board is on top, with the 14-bit up counter board directly underneath and the RAM board underneath that.

FIG 3.0 Circuit Board Layout (Top 1)

FIG 3.1 Circuit Board Layout (Top 2)

3.3 SUBJECTIVE PSYCHOACOUSTIC TESTING

Subjective testing involved setting up the processor in a room that was conducive to a normal listening environment. For the purpose of this demonstration, two separate integrated domestic hi-fi amplifiers and four speakers were used. For an enhanced effect a sub-bass unit was also installed. Refer to FIG 3.2.

FIG 3.2 Room Layout for Psychoacoustic Testing

Four mediums for playing music on were provided; CD, vinyl, cassette and DAT.
The CD player was to be the principle source of music in the subjective testing and as such the processor first had to be aligned up to it.
Domestic CD players may not give out equal voltages at their left and right outputs for the same output signal. To compensate for this a 1kHz tone from a recognised test CD was played into the processor. The balance trim-pot (refer to section 2.2.1) was tuned so that the surround outputs of the processor were at a minimum. This ensures that only out of phase information appears at the surround output.

3.3.1 Objectives

There were a number of objectives for the subjective tests, but principally it was to discover whether or not this method of producing surround sound gave an effect that the listener would find enjoyable.
Secondly it was to try and decide if there was a particular type of music to which this was best suited, or conversely whether there was any particular types to which it was not suited.
Finally it was to call upon the listeners previous experiences of other such systems to make a comparison, and also to simply explore the commercial viability of this system.
The listener was also allowed to make any comments that they felt appropriate.

3.3.2 Questionnaire and Test

For the actual subjective tests a questionnaire was produced (APPENDIX E).
The questionnaire was self explanatory, but a verbal summary of the test was also given.
Firstly it required the listener to give their name and gender, and then to say if they could hear equally well in both ears or not.
Essentially the listener was played two separate pieces of music. The first was a pre-determined piece which was known to create an interesting effect when reproduced in surround sound.
The second piece was a piece of music chosen by the listener.

Each piece was first played in normal two channel stereo, and then again with the surround sound switched in. By playing the piece in normal stereo first of all, it gave the listener the opportunity to hear the piece if they had not heard it before and also to accustom the listener to the listening environment, even if they had heard the piece before.

In total the listener was played music four times; stereo then surround for the first piece, and the same again for the second piece. Due to time constraints the listening time was restricted to two minutes per item, i.e. 4 x 2 minutes in total.

The questionnaire was allowed to be filled in at any point.

Although material was available which was recorded in different formats e.g. ambisonic, Q-sound, etc, etc, only conventionally recorded material was used in the tests.

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