Film-Tech Forum ARCHIVE: Audio codecs.

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Topic: Audio codecs.

Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 02-23-2006 06:49 AM

There seem to be quite a few people here with an audio/broadcast background, so somebody may know the answer to this.

What, if anything, are, or were, MPEG layer 1 audio and Dolby AC1 and AC2 used for.

What is a typical bitrate for 2 channel layer 1?

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Robert Minichino
Master Film Handler

Posts: 350
From: Haskell, NJ, USA
Registered: Dec 2005

posted 02-23-2006 07:05 AM

The "PASC" compression used in the DCC (Digital Compact Cassette) was essentially MPEG-1 Layer 1 audio at 384 kb/s.

I believe Dolby AC-1 was a non-perceptual ADPCM encoder. Here's what Dolby has to say on it:

quote:
The first Dolby digital coding system, Dolby AC-1, was introduced in 1984. It was adopted beginning in 1985 in a number of direct satellite broadcast and cable distribution systems. Encoding units are manufactured by Dolby Laboratories, while the decoder is licensed. Dolby AC-2, a more sophisticated system providing full professional quality audio, was introduced in 1989. It has since become particularly popular with music recording and film studios for interconnecting widely separated facilities via economical ISDN lines for remote monitoring, dubbing, and other applications. Dolby AC-3, now known simply as Dolby Digital, was introduced in 1992; it was developed specifically for multichannel applications, including film sound and digital surround sound in the home.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 02-23-2006 12:20 PM

AC-2 also found its way into several broadcast specific compression engines like Marti's STL system for transporting audio from studio to transmitter locations.

The codecs we use are made by Moseley using the APT-X codec from the 80's. These dont sound that good [Frown]

Thankfully we live in the era of true uncompressed audio transport systems, like the starlink, which provides 4 channels of uncompressed 15KHz audio and two serial data pipes, all in the space that used to occupy one FM composite channel [Smile]

Other manufacturers are using the 2.4 GHz band to provide a 45MB/s for STL use, and a remote internet connection [Big Grin]

Josh

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