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 (root mean square) average of the SPL values of those traces which are selected when the button is pressed. That means the dB values are converted to linear magnitudes, those magnitudes are then squared, summed and divided by the number of measurements, the square root of the result is taken, then the value is converted back to dB. Phase is not taken into account, measurements are treated as incoherent. The frequency range of the averaging result covers the region where the traces 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). If only a single trace is selected the result has the magnitude data from the source measurement and no phase data.

All SPL Actions

The Actions panel for the All SPL graph has these controls, there may be more or fewer controls depending on the measurement type.

All SPL Actions

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. Either of the traces may also be inverted (magnitude, phase or both). Division and inversion can be restricted to a frequency range with the response left unchanged outside that range. 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 neither has 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. If one trace has an impulse response and the other does not the result will have an impulse response. This could be used to merge a cal file response with an IR or apply a target response adjustment to an IR.

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). There is also a dotted trace which shows the result of a summation of the measurements ignoring phase. When the alignment tool is opened the All SPL graph selections change to show only the traces being aligned. Other traces may be selected in the graph legend if desired. The original trace selections are restored when the alignment tool is closed. There are two sliders for delay adjustment of the B measurement, one for coarse adjustment and one for fine to provide a wide adjustment range. The tool can operate in phase or impulse alignment modes.

Alignment tool phase mode

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.

Alignment Tool - phase alignment

When Show phase traces is selected in phase alignment mode 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 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.

Alignment Tool - impulse alignment

Alignment tool impulse mode

When Show impulse responses is selected in impulse alignment mode the All SPL graph is split with the SPL traces at the top and impulse responses for the two selected measurements at the bottom. To perform impulse alignment the responses are filtered at the cursor frequency with a 1/3 octave zero phase filter, the filtered responses are then aligned. The time span of the filtered impulse response graph adjusts to suit the alignment frequency.

Alignment tool impulse

The Align IRs at cursor button applies the filters at the cursor frequency and cross-correlates the responses to determine their best alignment. The alignment result may require inversion of one of the responses, which is evident in the impulse response display above. Here is the response after inverting the polarity of the subwoofer trace.

Alignment tool impulse inverted

That ability to ignore polarity in finding the best alignment of the responses is an advantage of the impulse alignment mode, but it may struggle to align the filtered responses in an environment with strong modal resonances near the chosen alignment frequency as the resonance may dominate the filtered response.


The IACC (Inter-Aural Cross Correlation) panel is used to calculate the early, late and full IACC values for a pair of binaural measurements. The zero time for the measurements is taken as the earlier of the two measurement IR start times. The division between early and late is 80 ms later. The end of the "late" period is 500 ms or the end of the Schroeder integral (where the integral falls into the noise floor), whichever is later. REW does not change the alignment of the measurements, if they need to be aligned the Cross corr. align option may be suitable. The measurements are filtered with one octave, zero phase bandpass filters of the chosen order.

IACC panel

All SPL Controls

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

All SPL Controls

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.

The IEC 263 ratio control allows the graph to be locked to a specified dB/decade aspect ratio. The aspect ratio is maintained by adjusting the margins around the graph as required.

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

Help Index