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

# Step Edit

As with Init Table, this button has completely different effects depending upon whether Meter or Match mode is active. Make sure you understand the basic approach as discussed in the Meter / Match Mode Control topic.

In Meter mode, you will do most of the calibration with Init Table. However, if you later decide that certain individual steps need to be adjusted, Edit mode allows you to change just the current step without causing all softer steps to get the same value as Init Table does.

In Match mode, Init Table resets the table to all the same step size, typically 0 (default), and you do the real calibration in Edit mode.

Toggle Step Edit on and then set Left Step to -1. The Right output will be held at step 0 for the duration of the calibration. We assume that Left and Right attenuators have identical step sizes, so the initial difference in loudness between channels is equal to the size of the dB step from 0 to -1.

We can find the size of the step by reducing the Right Level until the overall loudness matches, and expressing that Level reduction in dB. This is easily done via the dB / Step control, which takes care of the fraction-to-dB math. Just adjust the control until you hear a null (for the cancellation method) or a steady tone (for the alternating method) from the combined Left and Right outputs, and whatever value you see here is the dB attenuation from step 0 to -1.

Now set Left Step to -2. The dB value for the -1 step is automatically saved. Again adjust dB / Step until you again get a sound match. (Since most steps are dummy "no change" steps, you may not need to do anything if Init Table set them to 0 dB.) Repeat this procedure for all lower steps, without skipping any.

When you adjust dB / Step, you are adjusting the Right effective Level to give the indicated dB reduction relative to the prior step. If the prior step is wrong, you will end up inadvertently setting the current step wrong as well. For example, let's say that two adjacent attenuator steps are both really 1.5 dB each, but you erroneously set the first (louder) one to 2.0 dB. When you go to adjust dB / Step for the second one, you will end up setting 1.0 dB in order to get the proper total of 3.0 dB. The error won't continue to propagate to subsequent lower steps.

GO: