4 Replies Latest reply: Jun 17, 2009 11:08 PM by rkaufmann87
kl2999 Level 1 Level 1
My new IMAC 2.66gh 24" is coming. Just wondering if the IMAC can output true bit stream audio signal through the toslink cable. I have a Logitec 5400 THX 5.1 Speaker system support THX, Dolby Digital, DTS hard decode. What I heard from other website saying is IMAC can only output 2.1 channel audio sound through optical. If that is true then my 5.1 speaker system is useless.

IMAC, Mac OS X (10.5.7)
  • rkaufmann87 Level 9 Level 9
    You were given incorrect information, the iMac supports AC-3 which is Dolby Digital 5.1 by definition. Assuming the output is 5.1 and you are connected with a toslink connection you will get 5.1 sound. The specifications on the iMac are:


    Note the section on S/PDIF optical digital output


  • kl2999 Level 1 Level 1
    Certainly it will output any compressed 5.1 audio through the TOSlink. Perhap I should clarify my question, will the IMAC output "Bit Stream" (uncompress audio signal) to my speaker and decoded it through the hardware decoder in the speaker amplify? In other word my speaker would display DTS decoding when I play a DVD movie that has DST sound. Sorry for the confusion.
  • den.thed Level 7 Level 7
    Hi Kl2999

    Welcome to Apple Discussions

    Have a look at the > [iMac Audio System Audio Developer Notes|http://developer.apple.com/documentation/Hardware/Conceptual/HWTechAudio/Articles/Audio_implementation.html#//apple_ref/doc/uid/TP40003978-SW281200331167]

    +*S/PDIF Optical Digital Output*+
    +The S/PDIF optical digital output is automatically selected when an S/PDIF optical digital output device is detected on the external combo audio port. The S/PDIF optical digital output supports PCM and AC-3 audio formats with the following stereo data stream characteristics:+

    +PCM: 16, 20, or 24 bits per sample at sample rates of 44.1 kHz, 48 kHz, or 96 kHz+
    +AC-3: 16 bits per sample at sample rates of 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, or 192 kHz+
    +The S/PDIF optical output channel status conforms to IEC 60958-3 consumer mode digital audio.+

    +During playback of a 1 kHz sine wave (S/PDIF output format at 0 dBFS output level, 44.1 kHz sample rate, 24-bit sample depth, unless otherwise specified) the digital audio output has the following nominal specifications:+

    +Jack type: 3.5 mm (1/8”) stereo combo+
    +Digital audio signal-to-noise ratio (SNR): > 130 dB+
    +Digital audio total harmonic distortion + noise (THD+N): < -130 dB (0.00003%)+

  • rkaufmann87 Level 9 Level 9
    The specifications don't mention DTS, I am familiar with that format however it doesn't look like it is supported on the iMac. Please read over the specifications as Dennis noted. Most recording that have DTS also have DD 5.1 so if you are playing something recorded in DTS chances are excellent it will also have a DD 5.1 soundtrack as well.