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       SECTION 9.2                                                                       Sounds




                      TABLE 9.29 Additional entries specific to a sound object
KEY     TYPE          VALUE

Type    name          (Optional) The type of PDF object that this dictionary describes; if present, must be
                      Sound for a sound object.

R       number        (Required) The sampling rate, in samples per second.

C       integer       (Optional) The number of sound channels. Default value: 1. (See implementation
                      note 150 in Appendix H.)

B       integer       (Optional) The number of bits per sample value per channel. Default value: 8.

E       name          (Optional) The encoding format for the sample data:
                        Raw          Unspecified or unsigned values in the range 0 to 2B − 1
                        Signed       Twos-complement values
                        muLaw        μ-law–encoded samples
                        ALaw         A-law–encoded samples
                      Default value: Raw.

CO      name          (Optional) The sound compression format used on the sample data. (This is separate
                      from any stream compression specified by the sound object’s Filter entry; see Table
                      3.4 on page 62 and Section 3.3, “Filters.”) If this entry is absent, no sound compres-
                      sion has been used; the data contains sampled waveforms to be played at R samples
                      per second per channel.

CP      (various)     (Optional) Optional parameters specific to the sound compression format used.
                      Note: At the time of publication, no standard values have been defined for the CO and
                      CP entries.


       Sample values are stored in the stream with the most significant bits first (big-en-
       dian order for samples larger than 8 bits). Samples that are not a multiple of 8 bits
       are packed into consecutive bytes, starting at the most significant end. If a sample
       extends across a byte boundary, the most significant bits are placed in the first
       byte, followed by less significant bits in subsequent bytes. For dual-channel ste-
       reophonic sounds, the samples are stored in an interleaved format, with each
       sample value for the left channel (channel 1) preceding the corresponding sample
       for the right (channel 2).

       To maximize the portability of PDF documents containing embedded sounds, it
       is recommended that PDF viewer applications and plug-in extensions support at

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