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Discussion Starter #1
I have a 2018 Dodge Challenger with the factory Alpine "premium" system (comes with factory amp). Originally, I had installed a Rockford Fosgate DSR-1, which handled the OEM integration and also served as the DSP. I've decided to replace the DSR-1.

So I will now be using the AmpPro 4 for OEM integration and a Helix DSP.3 for DSP. I already have an AmpPro 4 with the toslink adapter installed. Since the AP4 has an optical-out and the Helix DSP.3 has an optical-in, I'm trying to decide if I am better off going digital between the AP4 and the Helix or stick with analog.

The AP4 will be installed in the dash and the Helix will be installed in the trunk, along with a JL Audio 6-channel amp (XD600/6v2).

To me, it just seems that digital would be cleaner and easier. Instead of running (4) bulky RCA cables from the dash to the trunk, I could run a single optical cable - and the optical cable would eliminate any potential noise-related issues introduced between the two components. I do realize that I would lose head-unit fading and there is some talk about jitter, but is there really any reason NOT to go digital in this case? I have read multiple threads on here about digital vs. analog, but wanted to talk specifically about my install/gear (AP4 in dash, Helix DSP.3 in trunk, etc).

Thoughts or experiences?

Thank you!
 

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Personally I don’t see the issue with pinching signal from between the headunit and amplifier and routing that into the dsp direct, the dsp will enable summing of all the outputs if filtered, enable sub level control etc, the use of the ap4 seems a bit strange as it’s another conversion from analogue to digital if you see what I mean

Personally I’d go direct from headunit to dsp and the to amps (just because you have something doesn’t mean it needs to be used or it’s better if you see what I mean)
 

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If you just want 2-channel stereo, then run a Toslink cable.
However, if you want more than 2-channels (ie. front/rear fade ability), then you'll need to use RCA.
From a sound quality perspective, you likely won't hear a difference.
 

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Discussion Starter #5
Thanks for the replies. Digital it is then...

The use of the AP4 is required to keep all of the OEM functions (it's an OEM head-unit) and allows being able to control their volume, etc. Things like warning chimes, navigation prompts, bluetooth voice functionality, etc... That is why the AP4 is needed - for OEM integration purposes. I'm not interested in hacking away at the factory wiring and dealing with issues related to trying to do it without the AP4. So since I'm using the AP4 anyway, it just seemed to make sense to use the digital output it offers. Not concerned with losing fading control from the headunit (I can do that via the DSP if I really needed to). The only other thing that I'll "lose" is the ability to play warning chimes from the rear speakers (backup collision warning chimes) - they will now come from the front speakers instead.

Really, I just like the ability to use a single, thin cable instead of (4) bulky RCAs - as well as not having to worry about noise-related issues between the head-unit and the DSP in the trunk. It would be nice if I could just install the AP4 in the trunk as well, but they really don't have it setup that way - it's meant to be installed in the dash. I'm not aware of any "extension" cables made for it.
 

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I've tried both the TOSLink and RCAs of my AP4. While I didn't necessarily notice a difference in sound, it was nice to have a single cable to run (granted the RCA's are still in place), plus I just thought it was cool to have a digital signal going to the DSP. I'd say go for whatever makes your life easier on the install, that's what gets my vote.

All that said, I believe I read Skizer stating that he's had noise issues with the RCA outputs on the AP4, so I'm sure you'll get varying opinions.
 

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Discussion Starter #7
Does using the digital-in on the Helix effect any of the "FX" options or cause any other limitations on the Helix (using it for true rear-fill, etc)?
 

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Does using the digital-in on the Helix effect any of the "FX" options or cause any other limitations on the Helix (using it for true rear-fill, etc)?
The only limitation, is that; you only have a left and right stereo channel.
It basically replaces channel 1&2 of your Helix input. But that's all you get.

As mentioned; not a big deal for most applications. And it eliminates any potential noise issues.

The only limitation is if; your vehicle has front and rear parking sensors, and your rear parking sensors ONLY come through the rear speakers.

If the AP4 has the capability to sum all the parking signals (front and rear) into 2 channels... then you're fine.
 

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Discussion Starter #9
Ok, thank you. Yes, I do have rear parking sensors that normally only play on the rear speakers, but the AP4 does play those over the front speakers instead when using the toslink connection. Honestly, I may just disable the rear parking sensors - really not that important since the car has a backup camera (IMO).

I'm assuming the toslink connections only support 2-channel audio in the car simply because there is no volume control on digital signals (unlike analog signals), which means there is no way to "fade" (so it doesn't make any sense to provide rear signals) - is that the reason?
 

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I'm assuming the toslink connections only support 2-channel audio in the car simply because there is no volume control on digital signals (unlike analog signals), which means there is no way to "fade" (so it doesn't make any sense to provide rear signals) - is that the reason?
No.
The native format for Toslink is 2-channel stereo (uncompressed).
Toslink can carry a volume signal - assuming your AP4 can control the volume off your head unit.

For instance;
I have a mObridge DA3, which taps into my vehicle's head unit.
The mObridge handles all volume control, as well as all chimes, and everything else.
It works flawlessly, just as if everything were OEM.

From the mObridge; I run a Toslink cable to my Helix DSP.
I only get 2-channel stereo intot he Helix, but that's all I need.
Volume is still controlled by the factory head unit, and chimes come through all speakers.
 

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Discussion Starter #11
Sorry - what I just said was stupid. :) Of course, the AP4 allows you to control the volume via the head-unit volume control, even when using the toslink interface. Otherwise, I wouldn't be able to control the volume at all. :) The manual confirms this ("When used in conjunction with the APA-TOS01, the module an provide a variable 2-channel fiber optic digital audio output (TOSLINK)."

What I don't understand then, is why it can only do 2-channel audio - I mean home audio receivers can do multiple channels over optical connections - so why can't they do that with car audio systems? I guess it's more of a "supported codec" thing (cost/licensing reasons maybe)? Sorry, digital connections are all new to me in the car audio world. Since most vehicles don't use/need 5.1 or 7.1 audio, I guess it just doesn't make sense to support it in car adio equipment?

I know I read *somewhere* about the toslink signals not having volume information - maybe it was in the Helix DSP.3 manual.... I remember seeing a warning about it saying that the level will always be "full" when using the toslink connection.
 

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I guess it's more of a "supported codec" thing (cost/licensing reasons maybe)? Since most vehicles don't use/need 5.1 or 7.1 audio, I guess it just doesn't make sense to support it in car adio equipment?
This...
Dolby charges something in the area of $100K for the license to use their 5.1 codec.
Plus the fact that there is no reason for 'surround sound' in a vehicle...
Just not practical, or needed.
 

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Discussion Starter #13
Thank you - I appreciate helping me understand this all a little better. I have a lot to learn with the Helix DSP.3 - looking forward to it though. Definitely a different beast than my current DSR-1. :) Much more powerful - but with power comes complexity. So I need to keep reading up and playing with the DSP tool while waiting for the DSP.3 to arrive. :)
 

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Nick suggested that I use the Toslink cable because he's seen noise issues with the Pac unit using RCA's. So, that's what I did. I have no rear fill, so that's not an issue for me. You have to flip the #1 switch on the PAC unit to get the rear parking sensors to the front speakers. If you are going with the rear fill speakers, the sensor signal will come out of the rears as well...
 

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If going digital, as mentioned, your head unit may not be able to adjust the volume. This means you must get the director or the URC.3 in order to control the volume from the Helix. Just something to keep in mind that you may have to buy.
 
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