With the release of Disney’s Toy Story 3 comes the introduction of the 7.1DS sound format. This is a different 7.1 format than that introduced by Sony in the mid-90’s. The new format brings to light some problems that lie ahead for digital cinema sound.
First, an explanation of the oddity of sound format terminology. The “.1” of “5.1” and “7.1” refers to the subwoofer channel. At the time that this terminology rose to popularity, the subwoofer channel was to be compressed as a low bandwidth signal, implying that it would require a smaller number of bits than a regular channel. In the digital cinema world of uncompressed audio, this concept no longer has meaning. The subwoofer channel simply occupies a full bandwidth uncompressed audio channel. So when reading audio format terminology such as “5.1” and “7.1”, one should simply add the numbers on each side of the dot. Thus, “5.1” occupies 6 channels of sound, and “7.1” occupies 8 channels.
The introduction of a new 7.1 format pushes the limit of those installations that wish to support all formats. Digital cinema allows up to 16 channels of sound. The assignment table below, which incorporates the new surround channels introduced by Disney (Left Rear and Right Rear Surround) demonstrates that we have hit the ceiling where multi-channel accessibility is required:
|
Channel Number |
Channel Assignment |
|
1 |
Left |
|
2 |
Right |
|
3 |
Center |
|
4 |
Subwoofer |
|
5 |
Left Surround |
|
6 |
Right Surround |
|
7 |
Center Surround (EX) |
|
8 |
Ceiling (not formally assigned) |
|
9 |
Left Center (7.1 SDDS) |
|
10 |
Right Center (7.1 SDDS) |
|
11 |
Left Rear Surround (7.1DS) |
|
12 |
Right Rear Surround (7.1DS) |
|
13 |
HI (language 2) |
|
14 |
VI-N (language 2) |
|
15 |
HI (language 1) |
|
16 |
VI-N (language 1) |
Digital cinema was intended to invite creativity in creating new sound formats. Historically, sound has been a significant element in differentiating cinema from home. But the approach taken so far within SMPTE is not enough to deliver the intent.
Proponents of the individual channel labeling format now in development within SMPTE claim that this will solve the problem of adding new speaker combinations to those outlined above. However, all it will solve is the problem of documenting how unique combinations of channels are delivered in a 16-channel package. Channel labeling does not take into account how the cinema that wishes to accommodate all formats is to be wired.
The introduction of new audio processors with 16 outputs to accommodate the 16-channels of digital cinema only shows how limited in vision manufacturers can be. All it takes is one more channel to break these products for countries such as Canada. That one more channel could be from a movie utilizing the Center Top channel, or an additional sub-woofer channel, both of which have been a topic of conversation of late. When considering this problem, it’s clear that sound processors having only 16 channels of outputs are not enough.
The original concept for digital cinema was that no more than 16 channels would ever have to be delivered to the theatre. This is a very different constraint to that of having only 16 channels at the output of the cinema sound processor. Each channel in the distribution package would be individually labeled as to its speaker location, and the sound system would figure out how to route it. However, a common and open process has yet to be defined for transferring the channel label information from the media block to the sound processor. If a standard for this is to be introduced, now is the time. It would be a shame to allow proprietary methods to evolve.