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Digital Audio Signal Generator, Pt.3

In the March and April 2010 issues, we described the design and construction of our new Digital Audio Signal Generator. The final article this month has the driving instructions.

By Nicholas Vinen

Driving the Digital Audio Signal Generator is straightforward. In operation, it delivers an output signal (analog and/or digital, depending on the configuration) as soon as it is switched on and the LCD initially shows the current signal generation mode. There are five such read-outs, one for each mode: locked, independent, mixed, pulsed and sweep.

In each case, the Up and Down buttons change the current mode and the display adjusts to show the corresponding reading. Pressing the Select button (in the centre of the main cluster) switches the LCD from the signal generation mode read-out to the setting read-outs. When this is done, signal generation continues according to the last mode selected.

Changing the setting read-out (done using the Up and Down buttons) has no affect on the current signal generation mode. There are seven different setting read-outs. Pressing the Select button again returns the unit to the signal generation mode read-out.

In other words, the Select button toggles between the current signal generation mode read-out and the setting read-out. The active generation mode is always the mode which was last selected.

Left & right buttons

On most read-outs, the left and right buttons allow you to move a cursor across the display. The only exception is the Status read-out where these two buttons have other effects (more on this later). In practice, the cursor can only move to locations which show values that can be adjusted or activated.

When the cursor is visible, pressing the Up and Down buttons will modify the indicated setting rather than changing the current read-out. Pressing the Select button or moving the cursor past the first or last setting hides the cursor and the Up and Down buttons can once again be used to change the current mode and/or read-out.

This system may sound complicated but once you try it, it will quickly start to make sense. In other words, it sounds more complicated that it really is and the process is quite intuitive once you understand the basics.

The mute buttons

There are two additional buttons on the unit – Left Mute and Right Mute. Pressing them toggles the mute status of the corresponding channel at any time. For example, if you press the Left Mute button and the left channel is currently enabled, it will be disabled and vice versa.

The mute status is shown on the status read-out and also on each mode read-out. For sweep mode, if a channel is muted, an “l” (indicating the left channel) and/or an “r” (indicating the right channel) is shown at the top of the display. For the other four modes, a muted channel is shown by changing the minus sign in front of each amplitude setting to an underscore.

If you press the two Mute buttons simultaneously, the left and right channel settings will be swapped. This includes frequency, amplitude and phase (when applicable), as well as the mute status.

Table 1 shows what each generation mode read-out looks like by default and highlights all the settings that can be changed. There is also a description of the function for each setting.

More mode information

As stated in the original article, the output frequency can be set at up to half the sample rate (ie, 48kHz) in steps of 1Hz. Depending on which frequency digit you select with the cursor, pressing the Up and Down buttons will add or subtract 1Hz, 10Hz, 100Hz, 1000Hz or 10,000Hz.

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