Offline Measurements

Sometimes it isn't possible or practical to connect a computer to the system you wish to measure. In those cases REW's measurement sweep signal can be played back through the system by other means, the response recorded, and the sweep signal and response recording can be imported to generate a new measurement. This is done using the Import Sweep Recordings entry in the File menu.

Generating the sweep signal

The first step is to produce the sweep measurement signal that will be played back when making the response recording. It is generated from the Signal Generator.

Signal generator measurement sweep

Pressing the button to save to a WAV file brings up this dialog:

Measurement sweep save dialog

Using a timing reference signal is recommended for offline measurement. Set the signal level for the sweep and the timing reference (typically they are the same) and choose the sample rate at which the sweep signal will be generated - this should be the same as the sample rate at which the response will be recorded, or an integer multiple or fraction of the recording rate. Pressing OK brings up the dialog to choose the WAV sample resolution, 16 bit should be very widely supported, if the system you are measuring can play back 24-bit WAV files choose 24-bit.

Sample resolution dialog

Importing sweep recordings

Bring up the import dialog by using the Import Sweep Recordings entry in the File menu (or using the Ctrl+Shift+N shortcut).

Import Sweep Recordings

Load the measurement sweep file first, either browsing to the file location or dragging it onto the stimulus window. You will be asked to choose which channel to import, 1 is the left channel, 2 is the right. If the current mic and soundcard cal files specified in the REW mic/meter and soundcard preferences should be applied to the files you are importing (for example, if you made the recordings with a calibrated mic and the mic cal file is loaded in REW) select the Apply cal files box. An image of the signal waveform is displayed.

Now load the recorded response file. You can browse to the file or drag the file onto the response window. If you have more than one response recording you can drag them all onto the response window at once and a separate measurement will be generated for each. If the recording sample rate is an integer multiple or fraction of the measurement sweep sample rate the recording will be resampled to match the sweep rate before processing.

Import Sweep Recordings loaded

That's it, a new measurement will be generated from the recordings and can be processed in REW like any other measurement. The measurement notes will include the file names used to generate it and the measurement name defaults to the file name of the response recording.

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