XDR (audio)

XDR (expanded dynamic range), also known as SDR (super dynamic range) is a quality-control and duplication process for the mass-production of pre-recorded audio cassettes. It is a process designed to provide higher quality audio on pre-recorded cassettes by checking the sound quality at all stages of the tape duplication process. In this way, the dynamic range of audio recorded on an XDR-duplicated cassette can be up to 13 decibels greater.
History.
XDR was originally developed by Capitol Records-EMI of Canada in 1982 as "SDR" (Super Dynamic Range). Capitol in the USA then adopted the system for its cassette releases that same year, renaming it "XDR".
Process.
The XDR/SDR process involves many steps, the most prominent being:
As well as with EMI & Capitol Records, PolyGram and other labels also offered cassette releases duplicated with the XDR process.
Test Tones.
Several different tonebursts were used during the life of the XDR/SDR process.
Album ID.
XDR tonebursts tend to be at both the beginning of side 1 and end of side 2. Some XDR cassettes include a series of DTMF-like dual-tones after the second toneburst at the end of the tape which uniquely identifies the album. Each dual-tone is 65 milliseconds long and separated by 35 milliseconds of silence. XDR's dual-tones are a modified form of DTMF where each of the two frequencies is one-half the usual specification. 