All SPL Graph

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 rms average of the SPL values of those traces which are selected when the button is pressed. Phase is not taken into account, measurements are treated as incoherent. 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).

All SPL Controls

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

All SPL Controls

The controls are split into four groups:

The Actions for all selected measurements are:

Measurement Actions

The Measurement actions dialog has the following controls:

Measurement actions controls

The options for each selected measurement are to:

Trace Arithmetic

The Trace Arithmetic controls allow the chosen pair of traces to be added, subtracted, multiplied, divided, coherently (aka vector) averaged or merged. A 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 operations on band limited measurements which may have been decimated to a lower sample rate.

Trace arithmetic controls

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 and the traces will be treated as incoherent.

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.

Trace arithmetic notes

Alignment Tool

The Alignment tool allows gain, polarity and delay adjustments to be made to a pair of measurements with a live preview of the summed result updated as the parameters are changed (the preview uses log spaced data at 96 PPO so may differ slightly from the final result).

Alignment tool

When Show phase traces is selected the All SPL graph is split with the SPL traces at the top and phase traces for the two selected measurements and the aligned sum at the bottom.

Alignment tool phase

The Aligned copy buttons generate a copy of the selected measurement with the alignment gain, delay and polarity selections applied. Aligned sum generates a new measurement with the summed results of the alignment settings.

The Level phase at cursor button calculates the delay required to bring the first measurement phase trace to be approximately horizontal around the frequency of the cursor in the phase trace graph. Both measurements have the same delay applied so the relative delays required to align them are not affected. Shifting the phase traces in that way makes it easier to align them. The delay is only used to update the phase traces, it is not applied when using Aligned copy or Aligned sum. Undo levelling removes the levelling delay from both measurements.

The Align phase slopes at cursor button calculates the measurement 2 delay required to give both phase traces approximately the same slope around the frequency of the cursor in the phase trace graph, so they have approximately the same group delay. Note that the phase traces may still be far apart, particularly if one measurement is out of phase with the other. In that case inverting one of the measurements would bring the phase traces closer together.

The Align phase at cursor button calculates the measurement 2 delay required to bring both phase traces as close as possible to each other around the frequency of the cursor in the phase trace graph. Note that a better overall alignment might be achieved by inverting one of the measurements and then aligning phase, and/or by manually adjusting the delay.

Other Controls

The Trace options button brings up a dialog that allows the line type of the graph traces to be changed.

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 frequency bands is selected the audio frequency bands are shown in a stripe above the graph. The bands are:

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.

When impedance is being plotted the axis has a span from 0 to 1 kohm. If a larger impedance range is required the axis can be switched to logarithmic with a range up to 1 Mohm using the Use a log axis for impedance check box. If selected a log axis will be used wherever impedance is plotted.

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