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a) Dolby is preparing a firmware update for the DP569 encoder, which will allow encoding of bitstreams
using the Extended Bitstream Parameters feature that do not trigger this interrupt. This firmware
revision will be available in early January 2002 for DP569 customers.
b) In the meantime, Dolby has advised key content producers of the situation, and suggested that they
disable the Extended Bitstream Parameters feature for any new content that they are mastering.
4. Dolby's DP569 encoder is currently the only encoder product to support the Extended Bitstream Parameters
feature. The current firmware is operating correctly relative to the Dolby Digital bitstream specification.
5. Several recent DVD releases, including Pearl Harbor and Jurassic Park III, have been mastered using the
DP569 with Extended Bitstream Parameters enabled.
Technical Description of the Problem
The DSP provides an audio configuration change function, which may be used to inform the host that one or more
audio configuration parameters have changed in the incoming coded bitstream. In some products, audio
configuration parameter changes are used to trigger short mutes, so that the consumer does not hear audible glitches
during configuration changes.
Decoder products using such IC's can detect audio configuration changes in two ways:
1. During decoding, the DSP in use provides access to many bitstream parameters. By using a Solicited
Read Message protocol, the host can read the current values of any or all of these parameters, and
manually detect configuration changes.
2. The DSP may also offer an Unsolicited Read Message feature, whereby the host can be automatically
informed (via software interrupts) of changes in the audio configuration parameters. In order for this
function to be active, the host must enable the Audio Config Change Notification Enable feature in the
DSP IC.
If the Audio Config Change Notification Enable feature is enabled, the host will receive a software interrupt
whenever any of the audio configuration parameters change. The specific list of Dolby Digital parameters that
trigger this interrupt depends upon the version of the DSP. In the latest firmware version, the parameters that trigger
the interrupt are:
acmod, bsid, lfeon, dsurmod, dialnorm, and timecod2.
The timecod2 parameter was added to this list in order to represent the Dolby Surround EX mode flag, dsurexmod.
According to the Dolby Digital Annex D specification, dsurexmod is carried in the two most significant bits of the
timecod2 parameter (assuming the bsid parameter is set to 0x6). However, other fields are also carried in the
timecod2 parameter as well. In particular, the least significant bit of this parameter is used to carry the Encoder
Information parameter, encinfo.
In practice, the dsurexmod parameter should not change over the course of a particular program. However, the
encinfo parameter was designed to change frequently from one frame to the next. In typical content that has been
mastered using the Extended Bitstream Parameters functions, the encinfo parameter will change state every two to
three frames.
As a result of these frequent changes in the encinfo parameter, if the Audio Config Change Notification Enable
feature is enabled in the DSP IC, the host will receive very frequent change notification interrupts. These frequent
interrupts may cause problems in two ways:
1. If the host is designed to mute during audio configuration change events, the result will be frequent audio
dropouts. If the duration of the mute is longer than a few audio frames, then these audio dropouts may be
continuous.
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2. If the host is designed in such a way that it is unable to service these interrupts quickly enough, the system
may overflow and lead to a host shutdown or reboot.
About the Encoder Information parameter
The encinfo parameter was added to the Dolby Digital Annex D syntax in order to provide a way for Dolby to
perform quality control and verification testing on encoded content. This parameter uses a low-rate data channel to
convey a range of information about the encoder used to create the bitstream, such as the encoder version, the
encoder settings, etc.
In order to recover this information, special monitoring tools are used to capture this bit from frame to frame over a
large number of sequential frames. When these bits are assembled together, they form a larger buffer that contains
the various encoder information values.
About Dolbys upcoming DP569 firmware update
In early January 2002, Dolby will release to its DP569 customers a firmware update that disables the encinfo
parameter. All other Extended Bitstream Parameters features including the Dolby Surround EX mode flag will
continue to operate as they do currently.
