AVERAGER OPERATION:

• Average Start
• Average Skip
• Average \ Instantaneous Toggle
• Averager Control Menu
  • Mode
  • Sweeps
  • Artifact Limits
  • Remote Control
• Average Add and Average Subtract
• Joint Average Start
  • Joint Average Spectrum \ Wave Toggle
• Joint Averager Control Menu

AVERAGE START (Avg):

• When the requested sweeps have been acquired, the Avg highlight is removed, the Pause option is invoked, and the status message changes from AVG to DONE.
• Hitting the A-key while an average is in progress will abandon it and return to Live operation.
• Hitting Pause will temporarily halt the average, until hit again to unPause. While Paused, the partial average may be saved to a file or to trace memory just as if it was Done. The Avg highlight will remain to show that the average has not been completed, and that it will resume as soon as the Pause state is removed. The Avg key will be disabled during Pause... you must first unPause if you wish to abandon the average.
• The GREY PLUS key can be used to temporarily suspend averager operation for any reason. The trace will revert to instantaneous mode and the the status will show SKIP. You can use this when you notice transient artifact activity, or any temporary condition that might compromise the overall average.
• If a REMOTE CONTROL is installed and has been enabled via the Remote option in the Averager control menu, then this can function just like the Grey Plus key noted above, either manually via a hand-held control, or automatically with the proper sensor and interface.
• Backslash (\-key) will toggle between the average and the instantaneous view while the average is in progress, in case you want to peek at the incoming raw data. The status message will change from AVG to INST, but there is no effect on the average itself. The sweeps count will continue to increase, but will be shown in parentheses when you are viewing the raw input. When the requested number of total sweeps has accumulated, the averager will stop and automatically flip back to show the averaged result.
• You can also use the \-key after the average is done. The status message will then toggle between DONE and PAUSE, instead of AVG and INST.
• While an average is in progress, certain functions may be locked out to prevent confusing the averager. However, many are allowed that might confuse your results. Don't change things in the middle of an average unless you are prepared to interpret the outcome appropriately.

AVERAGE CONTROL:

AVERAGER MODE:

• True
• Expntl
• Peak (Spectrum only)
• Histogram (Waveform only)
• PSTH (Waveform only)

The Expntl (Exponential) mode is an indefinite-length operation, which will run until you hit Pause or exit by toggling the average off with the A-key. Here the Sweeps parameter changes only the effective time constant, not the duration.

The Peak mode is only available for the Spectrum Averager. It will run for the specified number of Sweeps unless you have set that value to 1, which will be shown as 'Cont' for Continuous mode. In that case, the Peak "average" will run until you exit by hitting the A-key again.

AVERAGER SWEEPS REQUEST:

Note that this is the requested sweeps value. The processed sweeps are shown in the counter above the right end of the trace area.

For Peak mode, if you set the requested sweeps to 1 you will see 'Cont' instead of the value. This indicates a special Continuous peak scan that will run indefinitely when you start the "average", until you specifically exit by toggling the Avg key off. (Note that there is no particular use to an actual Peak setting of only one sweep, since True would give the same result.) In Cont mode, the sweeps counter will count normally up to 65534, then show 'Cont Peak' above that.

AVERAGER ARTIFACT LIMITS:

A limit bar on the right edge of the trace area shows where the limits are set relative to full scale for the input range. This bar does not change with trace magnification, so if you want to compare to the incoming waveform in order to help decide where to set the limits, you should set the trace magnification for full scale.

Artifact rejection works on the incoming waveform data, even if you are doing spectral averaging. The limit bar will thus not be directly comparable to the spectrum display.

The artifact limits are separate for waveform and spectrum averaging, allowing you to keep setups ready for two different acquisition scenarios.

Artifact rejection is always in effect when averaging. If you don't want this, simply set the limits to full scale. Since nothing will ever be above these limits, no sweeps will be rejected. You can easily set full scale values by entering much larger numbers like '1k' and '-1k', and Daqarta will set only the maximums appropriate for the effective range.

AVERAGER REMOTE CONTROL:

For tips on construction and wiring of a manual switch, see Remote Control Switch Construction.

AVERAGE ADD (AvAdd) and AVERAGE SUBTRACT (AvSub):

For example, if the original average was 128 sweeps and you hit ALT-A without changing the request value, another 128 sweeps will be added. The sweeps counter will count up from 128 to 256 as the extended average proceeds, and the final result will be as if you had requested 256 sweeps in the first place.

On the other hand, if you instead hit SHIFT-A (AvSub), the second 128 sweeps will be SUBTRACTED from the average. The sweeps counter will still count up from 128 to 256, but any constant features of the signal will average down toward zero.

You might want to use AvAdd in cases where the result from the original average is not quite clear enough, and you don't want to waste the original sweeps. This might be the case where you have a limited time to collect data before conditions change, or where averaging is inherently slow because of some limit on how fast you can induce responses from the system being measured.

But the most powerful uses of AvAdd and AvSub are in special cases where the response you want to observe is contaminated by an undesired response or stimulus artifact. If you can arrange to produce the same desired response while obtaining an inverted undesired response (or vice-versa), you can use these modes to cancel the response you don't want.

For example, suppose you are recording electrical responses of the ear to acoustic tone bursts. (Always be sure to use proper electrical isolation techniques to prevent lethal shocks!) The raw response will contain a component called the Compound Action Potential (CAP) that represents the summed response of many neurons firing in synchrony with the start of the tone burst.

Many of these neurons fire regardless of the polarity of the tone in the burst... they just respond to the overall onset of the tone. But the response will also contain a Cochlear Microphonic (CM) component that has a waveform similar to the stimulus itself, which is thus inverted when the polarity of the stimulus is inverted. The overall signal is contaminated with plenty of noise that needs to be removed by averaging.

So if you average half of the desired number of sweeps normally and then flip the stimulus polarity before you average the remaining half with AvAdd, the CM portions will cancel and you will be left with only the CAP portion. Or if you used AvSub for the second half, the unchanged CAP portion would be subtracted away, while subtracting an inverted CM that would be equivalent to averaging the original CM alone.

Similarly, you could be looking at thermal effects in a loudspeaker driver at high power levels. The polarity of the driving signal doesn't change its heating ability, so if the drive signal is contaminating the temperature measurement, you can use the above trick.

Note that these options may not always be the best way to do this job. For example, if conditions are slowly changing during the average, the second half may not cancel the first half properly after you invert the polarity. This can easily happen in physiological systems due to electrode contact deterioration, anaesthesia wearing off, etc. Or you might be testing your loudspeaker outdoors and the weather changes.

In these cases AvAdd and AvSub may be helpful during the development phases of your experiment, but you way want to use something fancier for the real data collection. If you can arrange things so that the stimulus alternates polarity on each sweep, then all you may need is a normal average to get rid of the stimulus-like component of the response. This has the advantage that the two sweep polarities are near each other in time and thus more likely to cancel properly since the system has had less time to change.

AvAdd and AvSub may be used in spectrum Peak mode only when the Sweeps request is a specific number, not Continuous. They both function only to continue the same peak scan action for an additional number of Sweeps.

JOINT AVERAGE START (JntAv):

During the JntAv you may toggle freely between waveform and FFT modes to view those respective averages.

JOINT AVERAGE SPECTRUM \ WAVE TOGGLE:

JOINT AVERAGER CONTROL:

To set up a Joint average, you must set the Joint parameters in waveform and spectrum modes separately, which you can do simply by toggling between then with the F-key after you invoke the Joint Averager menu with CTRL-J.

Since a Joint Average involves two averagers running at the same time, certain compatibility issues are enforced. If both the waveform and spectrum Joint Averager menus have True modes set, then the Sweeps parameters are simply locked together: Changing Sweeps in one menu changes it in the other to match. In all other cases, the Sweeps settings are independent and function as for normal averaging.

The overall averaging operation will stop when either waveform or spectrum mode reaches its Sweeps request, although as usual in Expntl mode the Sweeps value is a time constant and not a specific count request. If both waveform and spectrum Joint menus are of indefinite duration (Expntl or Continuous Peak modes), then averaging will continue until specifically toggled off by hitting the J-key again.

The Artifact Limits for both Joint menus are locked together, so you can change them from either menu.

Similarly, Remote Control is enabled or disabled from either Joint menu.

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