Dolby Digital and DTS Audio CD

Today's audio standards are moving towards multi-channel sound, like AC-3 and DTS. While the audioCD standard (RedBook) hasn't changed to accommodate these new sound formats, it is still possible to "go around" the specification and put 5.1-channel sound into regular audioCD's. These discs can be played back in any CD or DVD player that has a digital output. The incoming stream should be recognized by most AC-3/DTS capable receivers.

• Usage warning
• About sampling frequency
• Required tools
• Step 1: decode the source AC-3 file
• Step 2: convert the sampling frequency
• Step 3: create a Dolby Digital Wave
• Creating DTS Audio-CD's
• Download AC3 and DTS samples to burn on CD-R

Usage warning

When you play back these surround CD's in regular audio equipment, you must be careful : the digital data stream present on the CD must never be interpreted as PCM audio and played back as such. This means first that you must never listen to the analog audio outputs of your CD / DVD player because the resulting high-amplitude static noise could potentially damage your equipment if it lacks protection. Therefore, you should always listen to the digital output. Secondly, it's not 100% sure that your receiver can recognize AC-3 or DTS CD's. So the first time you're trying to playback a disc, you must test to determine if it can. To do that, begin with the volume very low, start to play the disc and rise the volume gradually. See if you're getting static noise or normal sound. If it's normal sound, then your receiver can recognize the disc. Note that you have to test separately AC-3 CD's and DTS CD's.

About sampling frequency

The only problem with these surround CD is that they are limited in terms of sampling frequency by the audioCD standard. This means that your source audio must be at 44.1 kHz sampling rate. What is annoying is that 99% of all surround material you will find is at 48 kHz (like DVD soundtracks). So you must first convert the sampling rate to 44.1 kHz (more on this later).

Required tools

To create your own Dolby Digital Audio CD (DD-ACD), you will need software tools to:

• extract AC3 files from DVD-Video (see labDV ripping section)
• extract 6 channels from the AC3 (Sonic Foundry's Soft Encode)
• resample from 48kHz to 44.1kHz (Syntrillium's Cool Edit 2000)
• encode 6 PCM channels in AC3 format (Sonic Foundry's Soft Encode or Minnetonka)
• encode 6 PCM channels in DTs format (Minnetonka Audio's SurCode CD Pro DTs)

Now, let's start to create an AC-3 audioCD.

This will show how to make a Dolby Digital Wave file that you can import in an audioCD layout in any CD-writing software. Source is considered to be a 48kHz AC-3 file.

Step 1: decode the source AC-3 file

Using Sonic Foundry's Soft Encode program, you must decode your source AC-3 file to PCM.

Soft Encode will save each channel as RAW PCM in its temporary folder. To find which folder it is, go into "options->preferences".

With Windows Explorer, go to that folder and spot the series of files named "AC3??.tmp", where"??" can be anything. These files, in order, correspond to front left, center, front right, rear left, read right, LFE. Set all these files to read-only, to prevent Soft Encode from deleting them. After that, you can close Soft Encode.