Originally Posted by PrazVT
You are confusing digital signal processing with digital -> analog conversion. The HU doesn't have to decode anything to play an analog signal - it simply amplifies it and sends it to the speakers. I'm not sure about the Logic7 control though - who knows, it may convert the signal back to digital again, do some processing, and then spit out an analog signal again. But I'm not sure...
Logic 7, like other digital signal processors, require a digital source to properly process the source material. If you want to hear real/true surround sound, the source material must be coded properly for surround playback. The DSP processor takes individual digital channels and process's each separately.
Example: DVD. The surround sound audio tracks may be coded in 5.1, 6.1, 7.1, etc..., left/right, center, LF/RR, Rear center, sub, etc...
The source player sends digital audio code to the processor, it then process's each channel, adds any optional coding, such as creating 7.1 out of 5.1, then sends to DAC, which sends the signal to the amp section. Proper surround sound amplifiers have individual amps for each channel. Since most home systems use a powered sub, the .1 is an output to feed the sub.
In car audio, the sub would also have it's own amp.
You can feed a 2 channel analog signal to a surround processor, but what will happen is that the DSP will have to convert the analog stereo into digital, then artificially create individual channels to mimic a surround field. It's artificial and no where near as good as source material coded for true surround.
This is where surround in a car becomes artificial, when using stereo source music.
The Logic 7 can only create an artificial surround sound field as the stereo source material is not coded for multi-channel playback.
Some people like that artificial sound field. The algorithms attempt to create sound fields that may be pleasing to some people.
When I get my 335i with HK, I'll try the Logic 7 sound fields, but usually I find them more 'interesting' than good.
HK does describe attempting to create a proper sound field for every seating position, which would indicate some phasing control, not really "surround sound". Maybe there are some L7 settings that do just that.
It'll be interesting to find out.
If you use source material that has been coded for multi channel surround, then playback on Logic 7 will sound true to what the engineer or artist intended. There are audio CD's that have been coded for surround sound, such as "super audio cd/SACD" and "DVD-A/audio".
These are higher resolution formats that can be coded for stereo 2-channel playback, or surround sound multi-channel playback.
The format never caught on in the larger market, but audiophiles like them, and I think new material is still being produced. Many older classic albums have been re-engineered and processed to create a surround sound field.
So, you're right, the HU would not need to process an analog source, such as an ipods analog stereo output. It can just route the analog source to the eq, then amp section.
But, if you want surround sound/Logic 7 added to the source analog material, then the system has to convert the 2 channel analog to digital, then into the surround DSP, process the artificial sound field, then send the signal to the amp and speakers.
My 135i only has an analog 1/8" stereo in. Like others I run a stereo 1/8" male cable from ipod to HU audio in. It does sound fine, or as good as the source material is. Mp3's can have various quality level depending on the compression settings.
I didn't get the enhanced functions in my 335i. I still listen to CD's.
I will use my ipod more though, as the radio stations in the Chicago area really suck these days. We have a lot of "classic rock" stations along with lots of modern pop stations, and nearly nothing in between.
I'm hoping satellite radio will give me more, but I've heard that sat radio audio quality can really suck.