The Soundcard Settings panel is used to configure the audio input and output
used for measurement, calibrate the soundcard and establish the correct
levels for making measurements.

The various controls on the panel are as follows:
- Sample Rate
- The sample rate may be set to 48kHz or 44.1kHz, the default is
48kHz. Note that the lists of input and output devices only include
those devices that report they support the selected sample rate, if
your device does not appear in the lists try changing the sample rate.
On a Mac it may be necessary to select 44.1kHz to access any audio input
or output.
- Inputs and Outputs
- The input and output device lists show the physical devices that
Java has found that report they support the selected sample rate, along
with some OS virtual devices. The lists of inputs and outputs are specific
to the selected input device and output device. The
Default Device settings tell REW to request
the defaults that have been set in your OS (in the Sounds and Audio Devices
control under Windows or the Audio and Midi Setup utility under OS X).
When the default devices have been selected REW leaves all control of
the the audio inputs and outputs and their associated volume controls
to you, use the controls provided by your soundcard's mixer or OS controls
to set levels and select inputs and outputs as required.
- Input Channel
- REW only uses one soundcard channel to capture the output of your
SPL meter or mic preamp, the Input Channel
control tells REW which channel you have connected to. The default is
the Right channel.
- Volume Controls
- The Wave, Output and Input volume controls are only enabled if you
have selected specific input and output devices, have checked the
boxes to allow REW to Control output mixer/volume
and Control input mixer/volume and REW
has been able to obtain controls for the selected devices from the OS.
Under those conditions REW will set the volume controls to the levels
last used for measurement, mute all output sources except for Wave and
select the chosen input.
- Sweep Level
- The Sweep Level control sets the RMS level
at which REW will generate its measurement sweep, relative to digital
full scale. The highest level possible is -3dB FS (which has the peak
of the sweep at 0dB FS), a typical setting is -12dB FS (the default).
- Calibration Panel
- The controls in the Calibration
panel are used to calibrate the soundcard. The Browse...
button is used to select a calibration file, a plain text file which by default
has the extension .cal, though other extensions are also accepted. The
file format is detailed below. Clear Cal
clears the calibration data structures, all subsequent measurements
will not have any soundcard calibration corrections applied to them
and REW will not load any previously specified soundcard calibration
file on the next startup. Measure... starts a process of measuring
the soundcard response via an external loopback connection. Make Cal...
is used to save a measurement as a calibration file - this should only be
used with the results of a loopback measurement, and then only after
checking that the measurement is valid. The measurement data is saved
as a text file, with the SPL values offset to give 0dB at 1kHz. The file
is automatically loaded on startup and applied to subsequent measurements.
- Levels Panel
- The controls in the Levels
panel are used to set the output and input levels for measurement.
Levels can be set using either a subwoofer or one of the main speakers,
this is selected in the drop-down box in the panel. The
Check Levels... button starts a process of establishing and
verifying the levels. The Generate Debug File...
button generates a text file with information about all the audio devices
and controls that Java has been able to identify. If there are problems
configuring the soundcard for use with REW provide a copy of this
file along with a description of the problem.
Soundcard Calibration File Format
The calibration file is a plain text file which by default has the extension
.cal, though other extensions are also accepted. It should contain the actual
gain (and optionally phase) response of the soundcard at the frequencies given,
these will then be subtracted from subsequent measurements. The values in the
calibration file can be separated by spaces, tabs or commas.
- Each line of calibration data must have a frequency value and a
gain value, a phase value is optional
- Frequency is in Hz, gain in dB, phase in degrees
- The cal points can be at arbitrary frequency spacing, but each
line must have a higher frequency than the one before and there
must be at least 2 freq, gain data pairs
- Only lines which begin with a number are loaded, others
are ignored
- In comma-delimited files there must be at least one space after the comma
- Spaces before values are ignored
- The sample rate at which the data was generated can be indicated by having
a line which starts "Sample Rate:" (without the quotation marks) followed
by the sample rate in Hz. REW checks for this when loading a file and will
warn if the rate does not match the current soundcard setting - calibration
data generated at a different sample rate will not provide accurate correction.
Here is an example section of a valid file format:
Soundcard Calibration data saved by Room EQ Wizard V3.26
Source: SoundMAX Digital Audio, Line In, Right channel, volume: 0.075
Format: 48000Hz sampling, Log Swept Sine, 176ms pre-impulse, 1,000ms post-impulse
Dated: 28-Nov-2005 17:19:51
Sample Rate: 48000
0 -9.38
1 -7.69
2 -6.34
3 -5.22
4 -4.26
5 -3.48
6 -2.80
7 -2.20
8 -1.71
9 -1.28
10 -0.87
11 -0.55
12 -0.25
After a calibration file has been loaded it wil be applied to all subsequent
measurements. Loading the calibration file does NOT affect any data already
measured and does not affect any measurement data that is imported. The
graph display is updated to show the calibration curve, offset to lie at the
current Target level.
Linear interpolation is used between calibration points. Outside the range of the
calibration data the behaviour depends on whether C weighting compensation has
been selected. If C weighting compensation is selected, C weighting curve figures
will be used for frequencies above or below the range of frequencies in the
calibration data. If not, the calibration values for the lowest frequency in the file
will also be applied for all lower frequencies and the calibration values for the
highest frequency in the file will be applied for all higher frequencies.
The calibration file name and path are remembered for the next startup, the
file will be loaded automatically when REW is started. A message confirming
loading of the file is given.
To stop calibration data being applied, use the Clear Cal... button.
Useful tip: To apply or remove a soundcard calibration file
after a measurement has been taken, simply load or clear the cal data
as required and press the Apply Windows button in the
IR Windows panel to recalculate the frequency response.
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