Coding Technologies

» see codingtechnologies.com as it lived, on the wayback machine

~ the last words ~

Coding Technologies AB was founded in Stockholm in 1997 by Lars Liljeryd. The European Patent Office's account of his career says he started it with three master's graduates, and what came out of it has a name only engineers use and an effect that almost everybody has heard: spectral band replication.

Audio compression until then worked by discarding the parts you were unlikely to notice. SBR went considerably further. It discards the entire upper half of the frequency range and transmits instead a small set of instructions for rebuilding that half out of the lower half once it arrives. The high frequencies you hear were never sent to you. They are constructed on your device from the harmonics that were. The EPO puts the saving at between 30 and 50 percent over the codecs that came before.

Attached to AAC this became aacPlus, published in 2001, and in 2003 it went into MPEG-4 as the High Efficiency AAC profile. 3GPP standardized Enhanced aacPlus for mobile networks in September 2004, pitched as CD-quality stereo at 48 kbps and plain stereo down at 32. XM Satellite Radio had already dropped its previous codec for it in 2002, and Qualcomm took it for handsets in 2004.

Dolby signed a definitive agreement for the company on 8 November 2007 and completed the purchase the following day, at a price its chief executive gave as approximately $250 million net of cash. The Swedish parent became Dolby International AB. The Nuremberg subsidiary, set up in 2000 with help from Fraunhofer IIS, became Dolby Germany GmbH. Both offices carried on working under the new owner, and the name was retired.

~ the record ~

~ how the trick works ~

Consider what a cymbal is, inside a file. It is a wide smear of high frequency energy with very little structure to it, and encoding that honestly costs a codec an enormous number of bits for a result your ear only checks roughly. SBR's bet is that you can describe the smear rather than transmit it. Send the low band properly, then add a small side channel saying which parts of it to copy upward and how loud. The decoder paints the top half back on.

There was a period when the size of an audio file decided whether I heard the song at all. Four megabytes over a home modem took enough of the evening to count as a decision, and in the Turkish internet cafes the clock on the counter kept running whether the transfer finished or not. Bitrate was not an abstraction in those years. That audio became tolerable over narrow connections at all comes down largely to this one idea, worked out by a handful of people in Stockholm and Nuremberg whose names none of us ever learned.

~ mp3pro ~

The idea was bolted onto mp3 first. Thomson licensed SBR and released mp3PRO in 2001, claiming a 64 kbps mp3PRO file sat somewhere between a 96 and a 128 kbps ordinary mp3 for quality. It had one fatal property. A player without the mp3PRO decoder would open the file perfectly happily and play only the lower half of the frequency range, so the same download sounded correct on one machine and muffled on another, with nothing on screen to explain the difference.

It was never standardized, no public reference implementation ever appeared, and the format drifted out of use while the underlying technique went into AAC and won. mp3PRO was the right idea attached to the wrong container at the wrong moment.

~ what you are listening to ~

Dolby got the patents and kept the people, and the technique went on spreading after the name stopped. Digital Radio Mondiale and satellite radio both carried it, mobile streaming was built on top of it, and Dolby shipped its own HE-AAC system, Dolby Pulse, from around 2008.

In 2013 the IEEE gave its Masaru Ibuka award for the work, to Liljeryd together with Kristofer Kjörling and Martin Dietz. The company that held the patents lasted ten years and has been gone for nineteen. The idea inside it is running on the device you are reading this on.

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