The following plots show audio spectra for 20 HD Radio stations. I recorded 20 seconds of audio from a Sangean HDT-1X tuner in split audio mode. The left-channel analog signal went to one output channel and the left-channel digital signal to the other. I captured the audio with Audacity, analyzed the spectra at 21.5 Hz resolution, and exported the data. I wrote a program to plot the difference between analog and digital. For ten stations I also plot the individual spectra. For two stations I add the source spectrum. I sampled typical program material.
Analog minus digital. 0–20 kHz. +10 dB to −20 dB.
Purple is digital, green is analog, and red is the aligned, normalized left source (FLAC file). 0–20 kHz. 10 dB/div.
20-second spectogram. 5.4 Hz resolution. RMS equalized. 80 dB color range. Click for digital/analog/source.
Click to check the variation for five pop songs.
Click for digital/analog/source.
88–108 MHz