Modifying (coding) the OEM Discover Media sound profile to make the output flat

[tomcollins]

I'm looking for some help in understanding if the following is possible.

MIB2 Head Unit - Hidden Sound Settings
The MIB2 (second-generation modular infotainment platform) head units (Discover Media) appear to have hidden, additional filters and EQ that we can not change without coding. This includes boosts to low and high that vary with volume, a high pass filter, other banded EQs. This is not the same as the user editable low/mid/high EQ.

For more info on see VW Discover Pro flat output?

I've fitted aftermarket speakers and an amp in my T6, and I'm about to add a sub. At some point I may replace the head unit, but will by stock OEM Discover Media for the foreseeable. Ideally I would like the OEM head unit to run a flatter output, without a high pass etc.

Modifying the MIB2 5F Sound Settings

The sound profile data for a MIB2 unit appears to be held in a 5F Infotainment System address.
Research of MIB2 Sound Datasets

If you can read this data out you can then load it into an editor such as 010 with these templates. And then write it back in to update the unit.

There are examples of people successfully removing the EQs etc through OBD / coding:
- VW Discover Pro flat output?

How can you do it?

You can use OBIS or Vag Com Pro to read/write the data. I have neither of these.

There are examples of people achieving this through 5F coding using a cheap ELM327 adaptor using the Car Scanner app. See Enabling *** & subwoofer control without VCP - FL success

I have the full Car Scanner app and a Carista adaptor. The app does not fully support the T6 platform (PQ?) at this time. I have been able to unlock developer mode, and also read a couple of 5F addresses but get an error when trying to read 0x003000 and 0x003B00.

What Next?

Has anyone done this already?

Is anyone able to read the 5F 0x003000 and 5F 0x003B00 addresses? How have you done this?

If you can read them and share the values I'd like to run them through the 010 editor templates to see if the data makes sense.

 

[Robert]

Have you seen and read these two SSPs?

VW OEM AMPLIFIER(R12) retrofit requires coding modification to the Infotainment Unit(J794) as well as appropriate data set upload with ODIS or VCP.

https://www.t6forum.com/downloads/ssp-561-the-t6-vehicle.51/download

https://www.t6forum.com/downloads/ssp-562-the-t6-infotainment-car-net.50/download

 

[Howzat]

I've just fitted a Helix DSP and was also after a flat output from the OEM unit prior to tuning.
I'd done a tune on the helix with the headunit set as default and you could see the helix EQ's were all over the show trying to compensate for the headunits settings so did some reasearch and found out the following.

Apparently this can be achieved real easy using OBD11 or similar by going into the multimedia section (5F) and changing byte 11 via long coding to "Sound_System_external_BOOSTER"
You then need to reboot the headunit by holding the on/off for 10 seconds ish otherwise the headunit doesn't switch off when you remove the keys.

Just done this and my previous tune definitely sounds different (flatter) so going back out to retry another tune.
Not sure if the headunits EQ will still change with the volume (hope not) and I believe there may still be some high pass filtering still going on (which I hope the helix can compensate for) but this option would be a hell of a lot easier than trying to read, change then rewrite the headunits EQ's via hex as suggested in the OP.

 

[n10n]

I've just fitted a Helix DSP and was also after a flat output from the OEM unit prior to tuning.
I'd done a tune on the helix with the headunit set as default and you could see the helix EQ's were all over the show trying to compensate for the headunits settings so did some reasearch and found out the following.

Apparently this can be achieved real easy using OBD11 or similar by going into the multimedia section (5F) and changing byte 11 via long coding to "Sound_System_external_BOOSTER"
You then need to reboot the headunit by holding the on/off for 10 seconds ish otherwise the headunit doesn't switch off when you remove the keys.

Just done this and my previous tune definitely sounds different (flatter) so going back out to retry another tune.
Not sure if the headunits EQ will still change with the volume (hope not) and I believe there may still be some high pass filtering still going on (which I hope the helix can compensate for) but this option would be a hell of a lot easier than trying to read, change then rewrite the headunits EQ's via hex as suggested in the OP.

Yes!

This setting also changes the HU outputs to lower level so amp’s low level inputs could be used. But will result in (harmless) speaker errors in scan as the HU will not see correct speaker impedances.

 

[Howzat]

Yes!

This setting also changes the HU outputs to lower level so amp’s low level inputs could be used. But will result in (harmless) speaker errors in scan as the HU will not see correct speaker impedances.

Interesting. So my helix is using the high level inputs from the headunits speaker outputs which were also high level.
Now I've changed the headunits setting as described earlier your comment suggests I'm now using the low level output from the headunit going into the high level inputs on the DSP.
What would be the implication of this?

 

[n10n]

Interesting. So my helix is using the high level inputs from the headunits speaker outputs which were also high level.
Now I've changed the headunits setting as described earlier your comment suggests I'm now using the low level output from the headunit going into the high level inputs on the DSP.
What would be the implication of this?

If you get enough output to the speakers and your volume knob in headunit has a usable range (ie the volume you would typically listen at is about 50 - 70% of the full range) just keep it as it is.

Quality-wise there’s probably not much difference whether DSP low vs high inputs are used. The DSP anyway converts analog to digital so as long as DAC input is happy you should be good. Amp high input *might* also look like a speaker from HU perspective so with luck you have no error codes - do a scan to check if you have eg Carista.

I’m not sure if HU outputs exactly line level in booster mode - but I do know that using it allowed me to use low level inputs of my Focal and ramp up the gain gnob in Focal a bit (not a DSP, just an amp). To me that made sense since larger part of the overall gain structure is then handled by the good quality amp. Does your Helix have input level adjustment knobs? How do they look like now?

 

[roadtripper]

I'm wondering if low level here just means a more limited volume range?

Traditional high and low level connections normally have different impedances which is more a physical property of the electronics driving them and not something easily altered in software, unless the head unit has two output stages that are physically switched between on the same set of connectors.

 

[n10n]

I'm wondering if low level here just means a more limited volume range?

Like @Howzat, my subjective opinion back at the time was that switching to external booster mode resulted in flatter sound.

I did not try to measure it in any way - I wasn’t really after a hifi setup, just reasonable clarity and less ear fatigue.

Traditional high and low level connections normally have different impedances which is more a physical property of the electronics driving them and not something easily altered in software, unless the head unit has two output stages that are physically switched between on the same set of connectors.

Most likely the amp in these head units is just a chip, not discrete components, and signal routing and stages used are controlled by software. I think it might well be some of the eq that tries to compensate crappy vw oem speakers is bypassed when configured for external booster - after all booster would be part of the better quality oem sound system.

 

[Howzat]

I just knew fitting the helix mini DSP to the stock headunit was going to take some fiddling but I think I'm nearly there now.
In my experience setting the headunit to 'external booster' does flatten the EQ and also drops the level but I think we've established this isnt a true "low level" output so I'm sticking with using the high level inputs on the helix. The helix has an input sensitivity screw on the rear so I think I can tweak this up to compenaste the headunits drop in level then also tweak the amp gain from the helix to drive my musway speakers adequately. Below is a video showing how the input gain is set on the helix mini DSP.

The last problem I need to fix is the fact my active subwoofer is driven from the rear speaker high level outputs from the headunit and that level is also reduced when 'external booster' is set so I now I'm hoping that enabling the rear fader option on the headunit will get everthing balanced up again BUT I have a niggling doubt that may not work due to the headunit not seeing any impedance for rear speakers. Oh the joys of upgrading audio from the OEM headunit.