## All SPL Graph

The All SPL graph is an overlay graph that shows all measurements (SPL and/or Impedance) that have been made. It allows an average to be generated of all selected traces or arithmetic operations to be carried out on pairs of traces to generate a new trace.

Average The Responses calculates an average of the dB SPL values of those traces which are selected when the button is pressed. Phase is not taken into account. The frequency range of the averaging result covers the region where the traces used overlap, for example if one trace was measured to 200Hz, another to 500Hz and a third to 1000Hz the average would range to 200Hz (to the lowest end frequency). New measurements (those made after the last average was generated) show new next to the trace value, whilst those included in the last average show avg.

### All SPL Controls

The control panel for the All SPL graph has these controls:

The smoothing control allows the fractional octave smoothing setting for all the currently selected traces to be changed.

The Measurement offsets control allows the chosen measurement to be offset either temporarily or (by using Add Offset to Data permanently.

If Show points when zoomed in is selected the individual points that make up the SPL and phase responses are shown on the graph when the zoom level is high enough for them to be distinguished (which may only be over part of the plot)

If Show modal frequencies is selected the theoretical modal frequencies for the room dimensions entered in the Modal Analysis section of the EQ Window for the currently selected measurement are plotted at the bottom of the graph.

The Trace Arithmetic controls allow the chosen pair of traces to be added, subtracted, multiplied, divided, coherently averaged or merged. If both the chosen traces have impulse responses, the result will also have an impulse response, however the sample rates must be either the same or related by an integer. For example, traces at 44.1kHz and 11.025kHz can be combined via an arithmetic operation, the result will have the higher of the two rates. This allows operation on band limited measurements which may have been decimated to a lower sample rate.

If the traces have incompatible sample rates, or either does not have an impulse response, the result will not have an impulse response, but it may have both magnitude and phase data if both the traces it was applied to had magnitude and phase data, otherwise the result will only have magnitude data.

The frequency span of the result of an arithmetic operation will be from the lowest start frequency to the highest end frequency of the traces operated on. Outside their frequency range traces are treated as being zero valued, with the exception of the divisor in a division operation which is treated as being unity outside its range. If the measurements actually have significant levels outside the measurement range the zero setting will generate oscillations in frequency and time domains, for best results use traces that span the full frequency range.

Notes

- For meaningful results measurements that have impulse responses or phase data should be properly time aligned before they are combined. An exception is the Merge operation, for which REW will automatically align both magnitude and phase at the merge frequency, adjusting the trace B time delay as required for the phase match. The amounts of the adjustments are shown in the notes of the newly generated measurement.
- The current impulse response window settings are used for each trace, the result uses the same window settings as trace A
- The result is smoothed using whatever smoothing was being used for trace A

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