Application description Spectrum Analyzer Signal Generator Audio Device Selection Input Channel Selection Calibration Sample rate FFT Number of points FFT Window type File management Restoring default settingsAppendix

User Guide

EasyRTA

Real Time Audio Spectrum Analyzer with Signal Generator

Calibration

Line IN / Line OUT Calibration

EasyRTA has an automated calibration procedure which allows a user to make very precise measurements. It is desirable to have a True RMS AC voltmeter, which has mV range, as an external calibration tool, but any decent AC voltmeter will also be good enough to achieve a straightforward calibration. Besides that, a stereo audio cable for interconnection of the Line Input and the Line Output devices is mandatory. It is desirable that the audio cable has a "Y" type adapter, which will allow a parallel connection of the AC voltmeter, but it can also be done with an ordinary cable without "Y" adapter if we first measure the output level on Line Output, and then connect Line Output to Line Input.

A user must take into account that audio cards in computers can differ substantionally in the quality and performance aspect. Some audio cards cannot measure signal levels of 0 dBu (0.775 Vrms) without distortion, some cannot output signal with a higher amplitude of -10 dBu (0.245 Vrms), etc. But, they can offer wide possibilities for measurements and fulfill most tasks. For more info, please see Appendix B.

Calibration procedure

  1. Connect Line IN to Line OUT on your Sound Card with stereo audio cable with "Y" adapter which will allow simultaneous AC Voltmeter measuring of audio output.
  2. In the EasyRTA Audio Device Selecton menu choose Line IN for the Input Device and Line OUT for the Output Device.
  3. Connect the True RMS AC Voltmeter with AC mV range to Line OUT or to the "Y" adapter to measure audio output.
  4. Set the Windows Sound Mixer volume level for the Line OUT device to 100%, and for the Line IN device to about 66% (more or less depending on the characteristics of your sound device).
  5. Press the [Calibration] button and read the AC rms voltage from your True RMS AC voltmeter (AC mV range).
  6. Enter the measured value from your True RMS AC voltmeter in mV rms as an integer number (without any punctuation marks).
  7. Press [OK] to accept calibration or [Cancel] to abort.

Mic Calibration

A user can perform audio measurements with an external microphone. Measurement microphones can have different frequency response characteristics, which can be compensated with an appropriate microphone calibration file. Calibration files can be loaded from EasyRTA, using the menu option "Audio I/O => Load a MIC Calibration File". EasyRTA has calibration files for 3 most commonly used types of microphones, which can be found in the folder "Mic Calibration Files". Depending on the measurement source, a user can choose to enable/disable microphone calibration in the "Audio I/O => Use MIC Calibration Correction" menu option.

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