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An innovation on polyphonic transcription
Interesting news from the New Scientist!...
Ivory encore for dead piano greats
* 22 April 2005
* Special Report from New Scientist Print Edition
* Mick Hamer
NEXT month music lovers in Raleigh, North Carolina, will be able to hear two of the greatest pianists of the 20th century in concert. Both the pianists, however, are long dead.
Zenph Studios, a software company based in Raleigh, has found a way to take a music recording and convert it into a live concert played on real instruments. The concert will be a completely faithful rendition of the original pianists' work.
Zenph resurrected a scratchy mono recording of Bach's Goldberg Variations, made by the Canadian pianist Glenn Gould in 1955 and a recording of a Chopin prelude by Alfred Cortot in 1928. Cortot died in 1962, Gould in 1982.
The breakthrough that Zenph has achieved is to extract the sounds from audio recordings and convert them into a high-resolution version of MIDI, the standard way of coding music for computers. To do so they had to tackle the problem of polyphonic transcription - distinguishing several notes played simultaneously. While researchers have been trying to achieve this for years, previous attempts have managed to identify at best 80 to 90 per cent of notes correctly - with about 10 per cent missing and another 10 per cent wrong (New Scientist, 22 December 2001, p 50).
Zenph now says it has found a way to do this, although for commercial reasons it won't release the details. But the company is confident enough to have organised the concert, at which a Disklavier Pro piano, one of a handful of concert grands that can record and play back high-definition Midi files, will replay Gould and Cortot's work. The piano will replicate every note struck, down to the velocity of the hammer and position of the key when it was played.
"We have only begun seeing excellent results in the past few weeks," says John Walker, president of Zenph Studios. "The results are note perfect." Walker has an impressive track record. Before founding Zenph in 2002, he was a leading developer of VoIP, the system that allows phone calls to be carried on the internet.
Walker says that the precise timing of notes is almost as important as identifying the correct notes. One of Zenph's final checks is to play back the conversion on the Disklavier and to make an audio recording of it. The engineers then play back a stereo version of the music: one channel has the original recording, the other has the recording of the conversion. "If they're different by even a few milliseconds, the ear immediately identifies that something's wrong - there's a slight echo effect," Walker says.
"Resurrected pieces include a scratchy recording of Bach's Goldberg Variations, and a recording of a Chopin prelude"
"The project at Zenph is definitely very, very interesting," says Anssi Klapuri of the Tampere University of Technology, Finland, who is one of the world's leading experts on polyphonic transcription.
The company is now working on a recording made at a private party by the jazz giant Art Tatum two years before his death in 1956. There are many recordings that have never been released because of some flaw, such as background noise or an out-of-tune piano. Zenph hopes that recording companies will use the new technology to make recordings from this type of material, or to clean up noisy recordings.
>From issue 2496 of New Scientist magazine, 22 April 2005, page 27
(http://www.newscientist.com/article.ns?id=mg18624966.700&feedId=online-news_rss20 <http://www.newscientist.com/article.ns?id=mg18624966.700&feedId=online-news_rss20> )
Dr Hüseyin Hacihabiboglu
I-Lab / CCSR
University of Surrey, Guildford GU2 7XH
Surrey, United Kingdom
Tel: +44 1483 683435
Fax: +44 1483 686011