Overlays Window

Overlays Window

The overlays window shows plots for all the currently loaded measurements. It is shown by pressing the Overlays button in the toolbar of the main REW window.
Overlays button

The overlay plots are selected via the buttons at the top of the graph area.
Overlay Graph Selector

The various graph types are:

SPL
All the measurement SPL traces
Predicted SPL
The predicted SPL for each measurement after applying any EQ filters that have been defined for the measurement in the EQ Window.
Phase
All the measurement phase traces
Predicted Phase
The predicted phase for each measurement after applying any EQ filters that have been defined for the measurement in the EQ Window
Impulse
All the measurement impulse responses
ETC
All the measurement impulse response envelope traces
Step
All the measurement step responses
GD
All the measurement group delay traces
RT60
All the measurement RT60 traces
Arithmetic
The Arithmetic plot allows the average of selected measurements to be generated and allows arithmetic operations to be applied to pairs of traces to generate a new trace.

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). Any of the traces which are selected when the Average The Responses button is pressed will be included in the averaging. 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.

Arithmetic operations are carried out on a pair of traces chosen via the graph controls. If both the 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

Separate Traces

The basic controls for the overlay graphs are described in the main Graph Panel help, but the Overlays window has one additional button.
Separate Traces Button
The Separate Traces button to the right of the graph selector offsets each trace downwards from the preceding trace to make it easier to distinguish individual features when the traces are at similar levels.

Graph Controls

The SPL graph has controls to apply smoothing to all the currently selected traces, a control to offset any of the traces and a box to select whether data points should be plotted. The trace offset moves the graph position, but does not alter the data so the legend values do not change. If the Add offset to data button is pressed the current offset value is transferred to the measurement data and the legend readings will update accordingly. If Show points when zoomed in is selected the individual points that make up the measured 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)

SPL Overlay controls

The Predicted SPL, Phase, Predicted Phase and Group Delay overlays also have a smoothing control. The Phase and Predicted Phase overlays have additional controls to wrap or unwrap the currently selected phase traces. The Phase, Impulse, Step and Group Delay overlays have a control to show data points when zoomed in.

Right clicking in the legend area of an overlay graph brings uo a small menu that allows all traces to be selected or all selections to be cleared.

Overlay Legend Popup

Hovering the cursor over the name of a measurement in the legend panel will bring up a tool tip showing the measurement notes.

Help Index