Parasound CD 1 CD player uses multiple readings to reduce errors
By David Szondy
April 2, 2013
Audio files may seem to have put paid to CDs, but new technology shows that, like vinyl, the format still has a few tricks left up its sleeves. CDs do a pretty good job of reproducing music, but many an audiophile claims the digital format lacks “warmth” and often suffers from tiny, yet detectable, imperfections that can be as jarring as serving Gordon Ramsay ketchup with lobster. The Parasound CD 1 player strives to eliminate these imperfections by ditching the conventional CD player in favor of a CD-ROM drive that spins CDs at four times normal speed in order to find and eliminate imperfections before they reach the speakers.
To call how a conventional CD player works as “simple” would be more than misleading, but it is relatively straightforward. As the CD player scans a disc, it converts the digital coding into an audio signal more or less in real time. True, there are algorithms and coding to try to mitigate errors, but the player’s job is essentially to act as a decoding and conversion device. This arrangement worked well enough to allow CDs to put vinyl LPs on the same shelf as Edison wax cylinders, but it still lets many disc errors slip by to the amplifier.
The Parasound CD 1, developed by Parasound of San Francisco in collaboration with Holm Acoustics in Denmark, uses a CD-ROM drive instead of a conventional CD drive, which turns it into something of a digital timewarp. The CD-ROM drive is connected to a passively-cooled Intel ITX computer with a large memory buffer that allows the player to store 30 seconds of playback audio. This gives the computer time to analyze the disc scans for errors without interrupting playback.
As the CD is spun four times faster than normal, the computer repeatedly scans the disc section by section, looking for errors by comparing each scan with a previous one. If no errors are detected, 30 seconds worth of audio data is dumped into the buffer and from there it goes on to the amplifier. If an error is detected and the player can’t resolve it before the buffer’s 30 seconds are up, it goes into “pre-interpolation analysis mode,” where the audio data is gone over one sample at a time until the bad fragment is found and isolated. According to Parasound, this always produces error-free data.
This multiple scanning and analysis also helps to reduce the “jitter” caused by timing errors between the digital disc scanning and the analog audio output. As the confirmed data is sent the buffer, it is synchronized with the CD-ROM input clock. This is then sent out of the player through an asynchronous USB interface where the output is timed by a second ultra-precise clock. To avoid any inter-DAC delays, the CD 1 also uses a single AD1853 Digital to Audio Converter (DAC) in stereo mode instead of one for each audio channel.
Not surprisingly, Parasound put a bit more into improving the sound quality than a new CD scanning system. There are three separate power supplies for analog and digital circuits, a six-layer DAC board for lower noise, proprietary software to ensure that the CD-ROM drive runs quietly, BNC digital cable outputs isolated by transformer couplings and massive aluminum partitions to isolate each function.
What also isn’t surprising is that the Parasound CD 1 doesn’t come cheap at US$4,500.
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