[Mizzou02RS]

I have a question...I will be purchasing a 20" G5 iMac soon and with it some new accessories...I know 2.1 speakers will work on an iMac, but will 5.1 systems work as they should or will I need special equipment to make theem put out true 5.1 sound?

Thank you.

[P]

It will work, provided your 5.1 receiver has an optical audio port.

[moodymonster]

the imac uses a mini-toslink, so you'd need that on one end of the cable (the other end depends on your amp). Also 'cause its a small plug the cable can't be too heavy or it'll damage the imac.

[SSharon]

Just in case you don't have digital . . .
http://www.m-audio.com/products/en_u...ater-main.html

[moodymonster]

it seems you need to turn on the amps decoding 'cause the imac doesn't do it. Previously with DVD players connected via digital coaxial the amp delivered 5.1 sound with no tinkering. With the imac we had to put the amp's own decoder on to get the extra (rear and center) speakers to work. Also works with HD trailers if they've got the extra channels, eg jarhead, lion the witch and the wardrobe.

[P]

Which program are you using, moodymonster? The OS supports decoding the 5.1 audio, but it's up to the program to do it. I know DVD Player should be able to do it, and I know that VLC doesn't because it's constantly on the to do-list. Don't know about Quicktime, but it ought to work.

When you say "decoding in the amp", it's not really the original 5.1 sound you're getting. When you do that (and I have that feature myself on my system, so I'm pretty sure this is the way it does it on yours as well) it generates the 3 other speakers and the sub out of the 2 channels it actually gets as input. It sounds OK for music, but for movies it's not as good.

[power142]

In Apple's DVD Player, the computer doesn't decode a Dolby Digital stream at all - it just passes it through the optical out to your receiver. This is why you don't get system sounds, etc, while using this capability. VLC has the ability to output the bitstream directly out the port too.

You can set the sound output in DVD player to use the system sound output instead of the digital output - but it will mix whichever audio track you are playing down to stereo (though it can still sound pretty good through a Dolby Pro Logic / II decoder)

[gnomexp]

On the same subject, I have a set of 5.1 speakers I use as 2.1ers on my Powerbook, but was curious if I could simply go all 5 on a PowerMac with OpticalOut.

From what everyone is saying, it'll work on all five for DVD player and a few other apps, but will all five speakers be used by default for system stuff (i.e. startup gong).

[power142]

No... the default audio on the Mac is stereo pcm (pulse code modulation), while Dolby Digital (and I assume DTS) can be passed straight through by certain apps. Unless you add an additional sound device (for example, one of the M-audio USB or PCI units), you'll only be pushing stereo out on either the Powerbook or Power Mac.

Also note that unless you have one of the additional sound devices that outputs each channel explicitly (or in pairs using 1/8" jacks), you will need a Dolby Digital decoder either built in to your speaker system or a receiver with one.

This is a shame... hopefully Apple will change with this with some new hardware in the future, especially since they seem to be pushing movie trailers from their own website with 5.1 channels, only in AAC format rather than Dolby Digital.

[cjarzabek]

I have a set of Logitech Z-680's and for anyone else out there with these, make sure that you change the audio option in DVD Player to pass the audio without doing any decoding on the Mac. If you do not change that option, you will only get 2 channels of information sent to the receiver. If you have changed this correctly, the LCD on the connection pod will read Dolby Digital / DTS when you are playing a movie instead of one of the various 2 channel modes (Stereo, Stereo x 2, Movie etc).