5 Audio Analyzer Measurement Functions124 Keysight U8903A User’s GuideThe SMPTE IMD value is computed as the ratio of the sum of the intermodulationharmonics amplitude to the upper frequency tone amplitude.Refer to Chapter 4, “Dual sine waveform” on page 98 for information ongenerating dual tones for this test.The SMPTE IMD measurement is shown as follows.Figure 5-12 SMPTE IMD measurementDifference frequency distortion (DFD)The DFD measurement is similar to SMPTE IMD, except that the two tones in thestimulus signal are of equal amplitude and are spaced closer to each other(typically 19 kHz and 20 kHz). This measurement also allows you to select eitherthe second or third order intermodulation distortion.
