Once the audio input and output have been chosen, the soundcard has been calibrated, the levels have been checked and the SPL reading has been calibrated REW is ready to make room response measurements.
Connections should be as explained in Getting Started, if connected to an AV processor, select the input to which the soundcard's output is connected.
The result of the measurement is displayed in the graph area, information
about the measurement appears in the
Measurements Panel. Measurements
are given a default name of the date and time at which they are made, a more
appropriate name can be entered in the box at the top of the measurements
panel
Notes relating to each measurement can be entered in the notes area, click
the Notes button
if the notes area is not visible
For details of the various ways of viewing the measured data, including averaging multiple measurements, refer to the Graph Panel help.
The headroom figure on the measurement panel shows how far away the
input is from clipping, and hence how much the sweep level could be increased
before clipping would occur. The figure is red if there is less than 6dB
of headroom (warning that the input is close to clipping), green between
6 and 18dB. A message is shown if the headroom is more than 18dB, as increasing
the Sweep Level or the AV processor volume would improve the signal-to-noise
ratio in the measurement which in turn increases the accuracy of the impulse
and frequency responses. Note that after making such a change it will be
necessary to use "Set Target Level" to establish the new reference level
for filter setting, and subsequent measurements will be at a higher SPL
on the graphs than those made before the change
If the room's resonances are very large the input signal level may exceed
the input range and cause clipping. If this occurs a warning is displayed,
as input clipping will cause errors in the derived frequency response. The
sweep level or AV processor volume should be reduced and the measurement
repeated. Note that after making the change subsequent measurements will
be at a lower SPL on the graphs than those made before the change.
If the signal levels are very low this may indicate a connection problem:
After measuring the response of a channel you can look at adjusting EQ immediately, or make other measurements first.
Note that some resonances which are very pronounced when measuring a speaker alone do not appear if a pair of speakers (e.g. Left and Right) are run together - this is because the positioning of the speakers in the room can prevent some resonances being excited (in particular, the odd order width modes will not be excited by content which is the same on Left and Right speakers if they are symmetrically placed across the width). Such resonances can often be left uncorrected, to identify them compare measurements from individual channels with those made with two channels driven at the same time (achieved on AV32R DP or AV192R by setting the Repeat Sig. entry in the TMREQ filter menu to Yes and selecting the channel which is to repeat the test signal, or on other processors by connecting both left and right soundcard outputs to the selected AV processor input or using a Y lead to drive two inputs at once).