Monday, January 9, 2012

A Xerox of a Poloroid of a Photo of a Painting

What format and bit rate should you choose for ephemeralizing your LPs?

While it may be popular, lossy compressed audio has its detractors. In an interview, Grammy-winning producer T. Bone Burnett likened its fidelity to the sonic equivalent of "a xerox of a poloroid of a photo of a painting."

[Image: low-res Beatles Sgt. Pepper album cover.]

Nonetheless, the 256 KBit/sec MP3 has become the de facto standard for purchasing and streaming music in the cloud.

Like WMA and AAC, MP3 is a lossy compressed format. (The three formats are interchangeable for the purpose of this discussion.) You can't uncompress an MP3 and get back the original audio. Some information is thrown away in the compression process to gain additional compaction over lossless compressed formats.

Lossless uncompressed formats incorporating linear pulse-code modulation (LPCM) capture a direct digital representation of an analog wave. "CD-quality" uses 16-bit samples taken at 44.1 KHz. The equivalent bit rate of 1411.2 KBit/sec transmits more than 5x the information in MP3 audio, with no loss due to compression. (See figure at right.)

Even a CD-quality copy introduces downsampling from the original. Most digital studio recordings are made with 24-bit samples taken at 96 KHz. The equivalent bit rate of 4608 KBit/sec transmits 18x the information in MP3 audio and more than 3x the information in CD audio.

It is possible to make 24-bit/96KHz recordings at home, 18x richer than a "good" MP3. Gigahertz computer clocks facilitate high sampling rates. Near-zero cost of storage makes compression unnecessary.  But is it worth generating and storing all those bits? Can anyone really hear the difference?

My Harman colleague Dr. Sean Olive, Director of Acoustic Research, is actively seeking a scientific answer to that latter question. My answer is simple: I don't care.

When it comes to information, more is always better. The digital transfer pipeline is software-driven. You may or may not be able to "hear" the difference, but your software tools can "see" the difference and work better when they have more to chew on. I'll use use the next couple posts to try to convince you to seek and preserve as many bits as possible when recording and processing, even if you ultimately choose a compressed format in which to store and enjoy your end products.

              Analog-to-Digital Restoration #8             

Title: Diamonds and Pearls
Artist: Prince & the New Power Generation
Genre: Soul and R&B
Year: 1991

Everything we've said regarding digital transfer of LPs applies identically to other analog source material. If you still have the equipment to play something, you can usher it into the digital future. I recently bought a like-new Denon DRS-810 at an estate sale for $25—a real find—to add to my recording station. My wife's equally like-new cassette copy of this Prince title is now dematerialized.

© 2012 Thomas G. Dennehy. All rights reserved.

1 comment:

  1. Do you believe you can hear the difference among compressed and uncompressed formats at various degrees of precision? Please leave a comment.