
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.

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

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
- 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
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.

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)

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.

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