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Discussion Starter #1
Hello All

This is my first thread here in DIYMA, and I'm not sure if I should be posting it here or in the "Dumb questions" section. Anyway, I think the intent of my question is more related to SQ, so, here I go:

I see a lot of discussions about RCA interconnects quality, how to avoid electromagnetic interference, signal losses, etc.. everything related to the disadvantages of having analog signal being transmitted through a cable. The bad is: at least for automotive sound, this is the only choice available, right?

So, why can't we have a digital interconnect between the head unit and the amp? An optical cable, for example. This way we could have a high-quality DAC inside the amp, with the option of bypassing/turning off the HU's one. No more low-voltage analog signal running through cables.

Of course I'm not intending to reinvent the wheel, obviously there must be strong reasons behind it, that make such a thing impossible/not feasible. So, I'd be interested in knowing which reasons are those... anyone?

Thanks in advance!!
Greetings from Brazil! :sunny::sunny::sunny:
 

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Disadvantages inlcude higher costs and having yet another item in the signal chain. I believe it was Power Acoustik that made an amp with an optical in; don't remember the model number though.

Also, why run an amp with digital/optical features when you can run a head unit with optical out to a processor with optical in followed by VERY short RCA's? My RCA's are about 10" long.
 

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I've watched audio change over the last 40 years and while the optical transfer would be the way to go, it's called costs. Not that it would be expensive to do, it wouldn't, but for a company to develope the standard and then sell their gear is the problem. Not many companies want to spend the money to develope a standard unless it's embraced by the rest of the manufacturers.
The best current example is the war between blueray and HD dvd. It lasted many years cost both groups a ton of money and then blueray won. HD dvd will slowly fade to nothing, all the money for R&D, sells and creating the platform is now wasted.
Sony learned this the hard way with beta tapes and VHS. Beta was the obvious better platform, but marketing did a pour job and VHS walked away with the prize. This time for the blueray wars, Sony had their hands in boths pools, they weren't going to be caught short.

If you look at TosLink, Toshiba link, you can see that most manufacturers have embraced it for the consumer market. You pay Toshiba for their technology and every device you install this on. But it's not the Toslink original data format they use, it's S/PDIF Sony Philips Digital InterFace.

In the electronics world, you develope a standard and every one pays you to use it. And no one wants to pay extra. So for the most part, they allow the big guns to develope the standard and then let the patents runs out and use them for free or minimal cost. Chips sets are a great example, you want dolby, pay me to put it in your amp. Patent runs out, we come up with another version, you pay me again.

So think about a digital standard between the head unit and the amp. Lets say you want all the eq done in the head unit. So you spend the time and money to develope this platform a long with a chip set that supports it for multiple amps. Lets say one cable for each amp. Sony comes around and uses one cable that feed multiple amps, repeater type, has provisions for eq in the amp. Motorola developes a chip set that does the eq in the head unit but leaves open a few bands for individual developement, contrls to other devices and the wars begin. Who's standard does every one embrace.

The worse thing you can do as a manufacturer is embrace a standard that doesn't get adopted. You buy a head unit that seems pretty cool only to find out a year later that it's not compatible with a new line of amps. You'll never buy that brand again.

Interface wars have been going on in the industrial world for many years and some of the major manufacturers have taken a beating over them. Some get adopted, Modbus is typical interface designed by Modicon, Allen Bradely has their own that has managed to survive for years. Honeywell ate mud on theirs as did many others. I've even worked with equipment specificly designed to do data conversions between manufacturers, one standard to another, all version specific. It's like trying to develope a machine that translates every language to a common one even taking into consideration dialects and accents.

So until some one developes a size fits all topology that every one can agree on, our RCA's are going to be our best bet. My money right now is on the HDMI format moving toward the automotive world. Why? the standard is there, it supports interfacing form device to device, automatic switching and high speeds. Firewire could be the standard, but USB has dominated it pretty hard.

But if you want to develope HDMI for an interface between your head unit and your amp, it cost 4 cents per device and a $10K royalty fee to do it. And that doesn't ensure that Alpine might just jump in bed with Sony for the I'link (firewire) and produce a standard where the royalty fees are very small and kick your butt into the dirt next year.

Hope that clears it up, follow the money, follow who is willing to take a chance, doesn't mean it'll be the best format for us, just means some one was willing to stick their neck out and take a chance.
 

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Discussion Starter #6
Yes, that's what I thought... all about standards... the digital world downside.

I think it's better to project & build my own than wait for them to do it :p
 

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Disadvantages inlcude higher costs and having yet another item in the signal chain. I believe it was Power Acoustik that made an amp with an optical in; don't remember the model number though.

Also, why run an amp with digital/optical features when you can run a head unit with optical out to a processor with optical in followed by VERY short RCA's? My RCA's are about 10" long.
No, it's not another item in the signal chain. It's actually FEWER items in the signal chain! You're bypassing at least one or two op amp stages by integrating the DAC and the amplification.

To the OP, there's no good reason why manufacturers don't do this. It's the way things SHOULD be done. All the processing can still be done in the HU (digitally), or externally. The only potential problem I see is bit depth. You need a volume control in the HU, and so it needs to sync some way with the DAC. So you'd need a standard so that HUs can talk to amplifiers/dacs, in a way more than just the ac3 signal, or whatever it would be. Can't just reduce the digital values to attenuate the volume unless you had really high bit depth (32 bits?).
 

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No, it's not another item in the signal chain. It's actually FEWER items in the signal chain! You're bypassing at least one or two op amp stages by integrating the DAC and the amplification.
^^ what he said :p

There are several benefits of running digital back rather than analog. This is the thought process behind Meridian Digital Home Speakers. Meridian's top of the line DSP8000 has four 24bit DAC's and 5 amplifiers inside each speaker. So not only is the analog signal short, the amplified signal is short as well. Kind of like putting a DAC and an amp at each speaker location in the car for each driver. Meridian is suppose to be working on their first ever car audio system with McLaren Automotive on the new MP4-12C. I'm sure knowing Meridians commitment to digital, it will have a similar design concept.
 

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No, it's not another item in the signal chain. It's actually FEWER items in the signal chain! You're bypassing at least one or two op amp stages by integrating the DAC and the amplification.

To the OP, there's no good reason why manufacturers don't do this. It's the way things SHOULD be done. All the processing can still be done in the HU (digitally), or externally. The only potential problem I see is bit depth. You need a volume control in the HU, and so it needs to sync some way with the DAC. So you'd need a standard so that HUs can talk to amplifiers/dacs, in a way more than just the ac3 signal, or whatever it would be. Can't just reduce the digital values to attenuate the volume unless you had really high bit depth (32 bits?).
I was speaking of the Power Acoustick model specifically and I have no idea how the DAC and op amps were placed or functioned. I don't even know if they ever actually released them for sale.
 
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