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, 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). 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.
The control panel for the All SPL graph has these controls:
The controls are split into 3 groups:
- Those which apply to an individual measurement
- Those which apply to all measurements currently selected in the graph legend
- Trace Arithmetic controls which apply to pairs of measurements
The Actions for an individual measurement offer the following:
- Offset the selected measurement either temporarily or (by using
Add Offset to Data) permanently
- Make a Minimum phase version of the selected measurement to use in
calculations - the copy has a minimum phase impulse response and the
same magnitude response and calibration data as the original
- Make an Excess phase version of the selected measurement to use in
calculations - the copy is the original measurement divided by a minimum
phase version of the measurement
- Make a new measurement with Response copy that has the same
response as the selected measurement - the copy has the same impulse
response and calibration data as the original but does not include
distortion data or equaliser settings, for example
The Actions for all selected measurements are:
- A smoothing control that allows the fractional octave smoothing
setting for all the currently selected traces to be changed. The
chosen setting is applied using the Apply smoothing button
- Time align, which brings all the currently selected measurements
into time alignment. If the measurements have been made with a timing
reference (a loopback connection or an acoustic timing reference) the
impulse response is shifted according to the measurement delay value,
taking into account any IR timing offsets which have been applied
since the measurement delay was calculated. Measurements which have been
made without a timing reference are shifted according to the estimated IR
delay. Time alignment can only be applied to measurements that have an impulse
- Vector average, which averages the currently selected traces taking into
account both magnitude and phase. It can only be applied to measurements that
have an impulse response.
- Align IR start, which aligns all the currently selected measurements
using their IR start times.
The Trace Arithmetic controls allow the chosen pair of traces to be
added, subtracted, multiplied, divided, coherently (aka vector) 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 operations 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 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
- 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 currently applied impulse response window settings are used for each trace. The
result uses the same window settings as trace A unless the operation was Merge B to A,
in which case the window settings for trace B (the low frequency portion) are used.
Any frequency-dependent settings are excluded, applying an FDW to the result would amount
to applying the window twice, as it is already applied to the data used to produce the result.
- The result of arithmetic on measurements that have compatible impulse responses is
smoothed using the measurement A smoothing, unsmoothed data is used during the calculations.
Other measurements use whatever smoothing they already had applied during the calculations
and the result is treated as unsmoothed (or 1/48 octave smoothed if data is 96 PPO).
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.