Specifications

CD-i FAQ 2000 Edition Revised February 21, 2001
Latest version and more CD-i info: http://www.icdia.org
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CD-i provides for 3 levels of ADPCM audio, all of which can be used either in mono or stereo:
• CD-Audio PCM, 44.1 KHz, 16 bit, all sectors, up to 74 mintues
• ADPCM Level A Stereo, 37.8 KHz, 8 bit, 1 in 2 sectors, up to 2.4 hours
• ADPCM Level A Mono, 37.8 KHz, 8 bit, 1 in 4 sectors, up to 4.8 hours
• ADPCM Level B Stereo, 37.8 KHz, 4 bit, 1 in 4 sectors, up to 4.8 hours
• ADPCM Level B Mono, 37.8 KHz, 4 bit, 1 in 8 sectors, up to 9.6 hours
• ADPCM Level C Stereo, 18.9 KHz, 4 bit, 1 in 8 sectors, up to 9.6 hours
• ADPCM Level C Mono, 18.9 KHz, 4 bit, 1 in 16 sectors, up to 19.2 hours
So, when ADPCM level C is used, only 1 out of every 16 sectors needs to be used for audio,
leaving all other sectors for other data such as video or animation. It's also possible to record
different audio channels at once, allowing for the seamless switching between for example
various langues. The disc may also be read from the beginning while decoding a different audio
channel, allowing for increased audio playing times, as indicated in the table.
A CD-i player equiped with a Digital Video cartridge is also able to decode MPEG-1 layer I and II
audio. MPEG is far more efficient in coding audio, resulting in even further decreased storage
needs while providing a highly increased audio quality when compared to ADPCM. This is
because of the fact that MPEG audio is based on PASC (Precision Adaptive Subband Coding,
the coding technique originally developed for DCC, Digital Compact Cassette), which uses the
characteristics of the human ear to only store those audio signals that are audible, and leaving
others out. CD-i offers a very flexible way of using MPEG audio (for example at various bit rates
and quality levels). CD-i cannot decode MPEG-1 level III, or MP3 files. A content developer
needs to be aware of the fact that MPEG decoding is not supported in a Base Case player, and
can only be used on player equiped with a Digital Video cartridge.
3.12.1 Does CD-i support Dolby Surround, Dolby Digital or MPEG Multichannel?
Dolby Surround is an analogue encoding technique that allows for the storage or center and rear
audio in addition to the normal left and right stereo signal. Every stereo audio carrier that provides
for a high frequency audio reproduction can use Dolby Surround encoding. In CD-i, Dolby
Surround can only be used for MPEG audio, since ADPCM does not offer the dynamic range that
is necesary for the encoding of the additional channels. Most movies use Dolby Surround, as do
several games such as Seventh Guest. Please be aware of the fact that Dolby Surround is an
analogue matrixing technique, which does not add extra discrete audio channels.
Dolby Digital and MPEG Multichannel are audio encoding techniques that allow for discrete
surround channels to be encoded individually. Ususally, this includes two front signals, two back
signals, a center signal and a low-frequency subwoofer signal. Both techniques are widely used
in DVD-Video. CD-i does not support either of them.
3.12.2 Can CD-i play back MP3 files?
No. The MPEG audio decoder in the Digital Video cartridge is only capable of decoding MPEG
layer I (used for example in the former Digital Compact Cassette - DCC) and layer II (used for
example in Video-CD). It is not capable of decoding layer III, the one used in the popular MP3
files. The CD-i's normal CPU (an 68000 at 15 MHz) is not capable of doing this in software, so it
probably is out of the question :-(
3.13 How does CD-i video work?
The video image of a CD-i player consits of four 'planes', which are shown on top of each other.
The first plane is used by a cursor, it size is limited to 16x16 pixels. The second and third planes
are shown beneath the cursor, and are used for full screen images. The fourth plane finally, is