Saturday, December 31, 2011

LPs and CDs Are Fraternal Twins

An LP and his digital twin.
Raise your hand if you think there are files on a CDDA disc (an "audio CD").

OK, put them down. There is some misinformation out there.

When you put an audio CD into your computer's drive, Windows Explorer will display a CDA (CD Audio Track) file for each track. If you double-click one, Windows Media Player opens and plays the track.

But the files don't really exist. Each one is a shortcut to where the corresponding audio track starts on disc. Explorer just calls them files because files are what it understands. Without the physical CD loaded, the "files" are meaningless.

A CD is a continuous laser groove of 16-bit digital stereo audio samples, starting at the inner edge and radiating outward. The implicit sampling rate is 44.1 KHz, meaning no time information needs to be encoded with the audio.

An LP is a continuous physical groove capturing an analog stereo waveform, starting at the outer edge and radiating inward. The implicit recording and playback rate is 33 1/3 rpm.

Both are round, have a hole in the center, spin while playing, and are read by a tracking sensor.

Thus, they are fraternal twins. A CD is basically a digital LP (played in reverse, but not saying Paul is dead). That's one reason CDs and LPs share common playback inconveniences, and why dematerialized digital playback has made the CD seem just as clunky as his analog twin.

In my professional life at Harman International, I manage development of multimedia infotainment/navigation systems for the OEM automotive market. Our newest systems don't even include a CD player. An iPod/USB interface is now standard, reflecting the market preference for dematerialized play.

But that didn't stop an OEM customer's test group from flagging a Harman system because "it didn't play CDA files." They thought that dragging and dropping CDA files onto a memory stick was equivalent to making an audio copy of a CD. We quietly buried the bug report as "not reproducible" (so to speak).

Our digital transfer process for LPs will produce more accurate results.

                Vinyl-to-Digital Restoration #1              

Title: The Survivors' Suite
Artist: Keith Jarrett
Contributing Artists: Charlie Haden, Dewey Redman (1931-2006), Paul Motian (1931-2011)
Genre: Jazz
Year: 1976

My interest in jazz got its start with a college housemate's copy of Keith Jarrett's The Köln Concert. But it really took off in grad school as I started mining through the ECM catalog at dear, departed Schoolkids Records in Ann Arbor MI. My jazz holdings stand now at roughly 250 titles, and you can trace a path back from virtually any of them to one of the four members of this quartet.

The most labor-intensive task in the digital transfer pipeline is extracting and isolating individual LP tracks. Not surprisingly, the task time grows linearly with the number of tracks on the disc. You're grateful for a title like The Survivors' Suite, where side 1 is track 1 and side 2 is track 2. Quick and clean.

© 2011 Thomas G. Dennehy. All rights reserved.


  1. Do you believe LPs and CDs are fundamentally alike or different? Please leave a comment.

  2. Fundamentally alike - as you have clearly demonstrated!

    Enjoying your blog

  3. the "natural" format of cd is a digital file, wav, 16 bits stereo 44khz. vinyl is analogue, it's not measured in bits, megabytes, samples per second or whatever, it's just sound, like in reality. a cd is a fake hologram of the music, no the real thing. they are nothing like the real records!