Daqarta
Data AcQuisition And Real-Time Analysis
Scope - Spectrum - Spectrogram - Signal Generator
Software for Windows  The following is from the Daqarta Help system:

# Timing Quantization Bias

Controls: Gen Dlg >> Stream >> Smooth TC >> Bias
Macros: TmBias, TmBiasMod

A value entered here is applied as a constant (DC) offset ahead of the quantizer. If the sum of the bias and the waveform exceeds the positive or negative full-scale range, the sum is clipped to the full-scale value.

If you set a positive value, you can force the quantizer to only use upper values from the range of steps; a negative value can force values from just the lower range.

This control is especially useful with binary noise, where Quant is set to 1 and the output is either positive or negative full-scale, depending upon whether the incoming random value is above or below 50 percent. For example, if you set Bias to a large negative value like -99 percent, then only rarely does the sum of the bias and the random source exceed the 50 percent threshold to produce a positive output; most of the time the output is negative. The result is a series of pulses having constant amplitude (+/- full scale) but happening at random times. You can use Step mode with Step Size to set the width of each random pulse. The Level and DC Offset controls on the main Stream dialog allow you to scale and shift this pulse train as needed.

To get pulses that are high a given percentage of the time, set:

```    Bias = (HighPercent - 50) * 2
```

For example, to get an output that is high 80% of the time, set Bias = (80 - 50) * 2 = 60.

If you use Burst with these binary pulses, note that the baseline is negative (or positive) full-scale, not zero as for standard waves. That means that the output will dip at the start of the burst, with the random pulses jumping up to the positive envelope value. To get a zero baseline, set the stream Offset to match Level.

Bias Modulation

The Bias label appears on a pushbutton to the left of the control. The button opens a Timing Modulator dialog that allows the Bias parameter to be modulated, either by a sine wave source with adjustable frequency and phase, or by some other stream source. You can set the base Bias parameter from that dialog, as well as the modulation depth.

The Bias modulator spans the same +/-100% range as Bias itself. When modulation is applied, the effective Bias value is equal to the sum of the base Bias value plus the modulator scaled by the modulator depth. For example, if the depth is 50% and the base Bias is 20%, the effective Bias will run from -30% to +70%.

The total effective Bias will be limited to the +/-100% range, so setting the base Bias to 80% in the above example will result in an effective Bias range of 30% to 100%, and it will linger at 100% for all the time the sum would have put it above that.

If you want the effective Bias to swing equally to positive and negative values, simply leave the base Bias at 0 and set the desired range with the depth control.

You can use Bias modulation to create realistic "Geiger Counter" effects: Without modulation, create binary noise as described under Quantization. Set Bias to get the desired "background" activity, then use modulation to simulate periodic or random increases in activity.

Macro Notes:

L.1.TmBias=50 sets Left Stream 1 Bias to 50%. L.1.TmBias=>1 increments the current Bias value by 1%, and L.1.TmBias=>-1 decrements it by 1%. Only +/-1 steps are allowed.

If the Timing Dialog is open, TmBiasMod=1 opens the Bias Timing Modulation dialog, TmBiasMod=0 closes it, and TmBiasMod=x toggles between open and closed. Note, however, that you do not need to open the dialog to set its controls directly. GO: