From the fine folks at Government Productions and Records here in sunny Portland, Oregon comes a re-creation of the XDR process tonebursts that preceded the (totally awesome!) music on many a cassette tape in the '80s. From Wikipedia:
The toneburst consists of 11 tones about .175 seconds in length, each an octave apart. These tones are recorded on the cassette, and are read during the duplication process to detect if there is any loss of any audio information.
From Government Productions:
After much hunting on the interwebs to find an example of the XDR Cassette Noise Reduction Test Tone for use on a clients song, Rob Weston decided to just go ahead and make his own. Then he figured, heck why not put it up here and let other people have it too...
Extra points to whoever actually owned a "cassingle". For the record, I had two.