Question about multichannel auto sound

[OldDog]

To start with a little background, I date back to the time of the discreet 4 channel reel to reel systems where there was a head for each of four channels. When you mixed you choose where the sound was to go and it was recorded on the appropriate head(s) to fit into the sound field.

Now a days we can do the same thing with Dolby AC-3 encoding and that works about the same from a 5.1 sound field placement point of view. I do this when recording for video.

My question is primarily about car stereos, if I put my old stereo CDs into my car the Alpine deck looks at the source and places different instruments throughout a basically 4 channel sound field. How does this work? Is it based on frequency, reverb, or what?

The reason I ask is to know if there is a way that when I am mixing a stereo CD I can determine where the instrument will play in the " 4channel" sound field?

Thanks,
Harry

[bozmillar]

There is no real standard for channel mapping in car audio. If you have a normal setup, then the rear speakers are just duplicates of the front speakers. Since the general market for car audio can be summed up with "more bass = better" not a whole lot of money is poured into development or marketing for actual quality car audio.

There are some car systems though that do have multichannel AC-3 decoders so that you can watch movies in your car in surround sound. They can also have Pro Logic II so you can get a matrix upmix of 2 channel content (like music).

[OldDog]

Perhaps it is ProLogic II at work as there is clearly some definition when I listen. Assuming that is the case, does anyone here understand the way the matrix works ( Yes I know, "No one can be told what the Matrix is, they must be shown" ). And more importantly how to mix for it.

Even my old dinosaur rock albums ( cds ) get a decent surround feel to them in the car and on my home theater system. ( Which definitly is ProLogic )

Best, Harry

[Danny Danzi]

Harry, you don't have surround in your car do ya? If you don't, what you're hearing is stereo imaging. If you played something in a car that was mixed for surround, there is no way you'd get surround of any kind unless you had some sort of button you push on your alpine that says "pro logic" or "surround". Please keep in mind, this is not true surround. What is happening is there is a delay and a slight reverb with a pre-delay inside the pro logic or surround feature that literally creates a HAAS type effect within the 2 channels. It's not the mix that is doing this, it's the Alpine component if it has this feature.

For example, there are soundcards for pc's that claim surround, but they aren't. They pre delay a reverb and place the second signal in a delay at about 6-11ms. This gives you the simulation of surround but is more stereo imaging.

If you played a true mixed surround sound piece of media in a normal stereo environment, the other channels will not appear on the system because the additional surround outputs are not present. True Surround components auto-sense the additional channels and route them accordingly, but if there is no additional channels because you are using a true stereo rig, they will not appear. Some egineers make the mistake to code additional channels in surround mixes, to stereo so that the additional channels are sent left to right. The problem with this is phasing can occur which is why mixing in surround is so difficult for inexperienced engineers to handle.

So it is my guess that if you have any type of surround or pro logic button present and the speakers you are playing through are not true surround, you are getting a form of stereo imaging because it would be impossible for surround to come out of car speakers. Your front and your back are handling 2 channels. Left front and Left back are exactly the same channel Left channel. Right front and right back are exactly the same right channel mix.

Unless you had your car speakers wired for independent channeling, there is no way to hear surround sound at all. But like I said, there are little buttons in systems that claim surround, but they aren't real...they are surround simulations demonstrating the pre delay in a verb and an actual timed delay creating a HAAS effect of stereo imaging.

Now, you could simulate this with a mix if you wanted to. But there is no way to place the sounds in a specific speaker in your car. You can go left to right and even widen the stereo field using something like the Waves S-1 or the PSP Stereo controller or enhancer etc. What these particular plugin effects do, is they take all the stereo tracks in your project and spread them wider. That means anything that has a stereo effect or tracks that were doubled and panned, will be wider in the mix.

The issue with this is the mix can become too separated because all the mono instrumentation will stay centered in the mix. So you could be left with guitars, back up vocals, keys, snare verbs, delays and anything used in stereo in your project, widened away from the actual instrumentation. Kick drums, snare, bass guitar, lead vocals etc...which are usually center panned instruments, would stay centered....but any stereo effects used on them would be super wide in the stereo field and separated.

Using these spacializer type effects like the PSP and Waves s-1 can give you that simulated sound that sounds similar to surround and is wider, but it cannot be controlled through L/R stereo as to where it ends up unless the mix is mixed in true surround and the system you are playing it on supports it. Hope this helps to clear up any of your confusion.

[OldDog]

Thanks for the feedback Danny,

Actually unless I am grossly mistaken, most modern car systems are four independent channels, LF, RF, LR, RR, but the source is simply stereo. I was trying to figure out if there was indeed some type of logic in there that said "> 2k goes tot he RR" for example or perhaps something that measured echo per frequency and placed things in the field that way ( ya I know a pretty far reach ). Something, anything that we could control when recording.

I think you answered that, that no, it is a slight of hand that gives me that "quad" feel to the system.

I swear that if I put in say "Dark Side of the Moon", the location of the chimes really do seem to bounce front to rear as well as left to right. Perhaps my brain is wired from the old quad recording to hear it that way!

Thanks again,
Harry

[bozmillar]

Well, it might have an upmix function. I don't know about other matrix decoders, but Pro Logic II and Pro Logic IIx do a pretty good job of extracting the right information from the stereo mix.

For film, back in the days of tape, the mastering engineers actually did their stereo mixes so that they would have the best effect after running through a pro logic decoder. There are different ways of downmixing multichannel content so PLII can make the most of it.

PLII looks at the phase coherency and a few other things to figure out what is supposed to go in each channel. You can make a two channel mix in such a way that you can "steer" certain sounds to different channels with PLII.

It's not discrete multichannel audio, but it does a pretty good job. That and mastering engineers use it as a reference when they are creating the 2 channel track, at least for film. For music, I'm not so sure PLII used as a reference.

[String7th]

Originally Posted by OldDog

I was trying to figure out if there was indeed some type of logic in there that said "> 2k goes tot he RR" for example or perhaps something that measured echo per frequency and placed things in the field that way ( ya I know a pretty far reach ).

Actually that's not far from the truth. But it's not as complicated as that. The cars built within the past 10 years have been better at speaker design for acoustics. From the source car stereos are simple 2-channel stereo, but the speakers will have in-line hi-pass filters and in-line crossovers to sound best in the part of the car they are in.
I found this out replacing the stock speakers in a 2000 Toyota Celica. The front speaker had a cross over to the woofer/tweeter, and the rear speakers had what's called a bass-blocker, which I'm sure dug out some specific frequencies.

All this causes the audio to sound like the guitar is coming from the front speakers and the bass and vocals are coming from the back. Because certain frequencies are being cut from certain speakers.

[leonAzul]

Originally Posted by String7th

Actually that's not far from the truth. But it's not as complicated as that. The cars built within the past 10 years have been better at speaker design for acoustics. From the source car stereos are simple 2-channel stereo, but the speakers will have in-line hi-pass filters and in-line crossovers to sound best in the part of the car they are in.
I found this out replacing the stock speakers in a 2000 Toyota Celica. The front speaker had a cross over to the woofer/tweeter, and the rear speakers had what's called a bass-blocker, which I'm sure dug out some specific frequencies.

All this causes the audio to sound like the guitar is coming from the front speakers and the bass and vocals are coming from the back. Because certain frequencies are being cut from certain speakers.

It could even be crudely done by reversing polarity on one of the tweeters. That's an old trick for "expanded" stereo in portables.

[Danny Danzi]

Originally Posted by OldDog

Thanks for the feedback Danny,

Actually unless I am grossly mistaken, most modern car systems are four independent channels, LF, RF, LR, RR, but the source is simply stereo. I was trying to figure out if there was indeed some type of logic in there that said "> 2k goes tot he RR" for example or perhaps something that measured echo per frequency and placed things in the field that way ( ya I know a pretty far reach ). Something, anything that we could control when recording.

I think you answered that, that no, it is a slight of hand that gives me that "quad" feel to the system.

I swear that if I put in say "Dark Side of the Moon", the location of the chimes really do seem to bounce front to rear as well as left to right. Perhaps my brain is wired from the old quad recording to hear it that way!

Thanks again,
Harry

Actually Harry, you very well could be correct in what you're saying/thinking/hearing. I really don't know for sure other than what my hunch is mostly due to never experiencing surround unless I was listening on a surround system or like I said, that simulation thing was going on. This of course doesn't mean I'm correct...and my apologies if I came off sounding like I knew the answer. I just have never experienced this other than what I've mentioned. It's definitely worth looking into, that's for sure as now I'm super curious about this. I'll call a few guru friends of mine and see what I can come up with for this.

[OldDog]

Originally Posted by Danny Danzi

Actually Harry, you very well could be correct in what you're saying/thinking/hearing. I really don't know for sure other than what my hunch is mostly due to never experiencing surround unless I was listening on a surround system or like I said, that simulation thing was going on. This of course doesn't mean I'm correct...and my apologies if I came off sounding like I knew the answer. I just have never experienced this other than what I've mentioned. It's definitely worth looking into, that's for sure as now I'm super curious about this. I'll call a few guru friends of mine and see what I can come up with for this.

Cool, let us know what you come up with.

Again, thanks to all who contributed to this. I have always been a sucker for surround and would love to get a handle on how we could manipulate it.

Best regards, -H