XDR (eXtended 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.
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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:
32 Hz, 64 Hz, 128 Hz, 256 Hz, 512 Hz, 1000 Hz, 2000 Hz, 4000 Hz, 8820 Hz, 11,025 Hz, 18,000 Hz
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.
As well as with EMI & Capitol Records, PolyGram and other labels also offered cassette releases duplicated with the XDR process.