Phase Meter
Phase Meter is used to measure the phase angle between two sine waves.
THD+n
You can measure Total Harmonic Dist noise (THD+n) with iAudioInterface2. To do this, the
App will generate one of several octave-band sine waves, which are routed to the device under test
(DUT). The output of the DUT is then routed back to line input of iAudioInterface2.
To measure the lowest possible distortion, the output level must be set close to the upper range of
the middle line input range, 8 dBu. Make sure that you keep the input level to iAudioInterface2 is as
close as possible to this level when you route the signal through an external device.
If you are generating a signal yourself, make sure that it is exactly the frequency that THD+n is set
to, and that the level is as close as possible to +8dBu, as shown on the AudioTools input level meter.
The App then subtracts the fundamental sine wave, and the resulting signal is compared to the full
input signal. The result is the THD+n.
For best results, and to measure the lowest possible THD+n, use the middle line input range if
possible. You may select the other ranges, but the minimum distortion that you can measure will be
greater than can be read using the middle level.
Impedance Meter and Impedance Sweep
To measure impedance, you need a special cable. This cable is a
¼
” TRS cable with the tip and ring
brought out to test leads, and the ground not connected (open).
You must use only this cable
configuration with the impedance test functions.
This cable is plugged into the line output
connector. The test leads are then connected across the load, and the generator is turned on. The App
then computes the impedance of the load and displays the equivalent wattage for the selected
voltage source.
The output of iAudioInterface2 is fixed in impedance testing. Before you set up for impedance
testing you must calibrate the impedance test. To do this, go to the impedance setup function, which
you can reach from either impedance test by tapping the wrench icon or pressing Setup.
Next, turn on the generator, disconnect the clip leads (maximum resistance), wait 10 seconds for the
reading to stabilize, and tap the Maximum button.
Now leaving the generator running, and clip the impedance test lead together (0 ohms). Wait 10
seconds for the reading to stabilize, and tap the Minimum button. Calibration is now complete and
you may use the function.
iAudioInterface2 User Guide
Page 13
