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Discussion Starter · #1 ·
Hello, I'm trying to Eq the high level signal i get from my factory HU to make it electrically flat. I already measured the headunits electrical frequency response and know the eq settings i would need to make.

Is there any way to do this on my helix dsp.3 and if not how are some other ways i can achieve this? I would like to keep the Factory Headunit.
 

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2016 Mazda 6 GT
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It's called ISA (input signal analyzer) and click on the IO tab. Look to the right of the screen and you'll see a 3 slider band symbol and click on it. That takes you to the ISA. From there it's pretty intuitive. Forget your measurements and use the rta that's there.
 

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remember, flat isn't necessarily needed. full range and free of phase/timing differences is what you are after. But yes, use the input EQ in the IO tab.
 

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If you don't need all 8 outputs for your speakers, and can spare 2, you could also loop back 2 outputs to a second set of inputs which will give you an extra 31 bands of EQ for each side. I'm not sure if that works on the Helix, but I used to do it on the miniDSP...
 

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Discussion Starter · #5 · (Edited)
Thank you for all the quick replies! I looked through the IO tab a few times and somehow missed the eq button every time! This looks like exactly what I wanted!

But skizer, Would it not be best to have identical signal going into the dps that is going into the HU (From phone) I understand the acoustic response is not meant to be flat, but the signal going into the dsp? If I'm playing pink noise it should be flat shouldn't it and then adjust the signals on each individual channel to get the desired curve?


also not sure how I would go about examining phase off of an RTA. Only way i know is through IR. Could you perhaps explain me to the process? also Would this not be something not to worry about until I'm time aligning individual channels?

Here is a picture of my measurement, made with Pink Noise 1/12 smoothing with about 50 averages. I used this Method to Measure:
Using TrueRTA and MobilePre to measure Frequency Response of headunits | DiyMobileAudio.com Car Stereo Forum

EDIT: This is a Toyota Rav4 2018 regular (not JBL upgrade) Headunit if anybody was wondering.

Rectangle Azure Slope Font Line
 

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Your rta has about a 25dB swing… something’s not right. Maybe measure again and just leave the mic fixed in one location.
 

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Discussion Starter · #8 ·
This is not a measurement from my Microphone this a measurement of my High level inputs right before they reach my helix dsp. No acoustics, just electrical. I wired in a TRS stereo connector to my High level inputs and used my sound card to measure it. I wanted to see if my Factory headunit was outputting a full, flat signal. I played Pink noise from an app on my phone and a file I downloaded on my laptop, both produced the same results. That is the measurement at max volume but it did not seem to change the shape of the measurement at lower volumes.

I'm going to try to use the built in ISA as you suggested before. I had no idea it was even in here!

Cutaway: I believe the pink noise is supposed to appear flat in REW as the graph is split much more by octaves, not by frequency. if the graph was evenly distributed between 20hz-20khz then it should appear with a downward slant. Correct me if I'm wrong though, but all the other people in the link I posted tests showed pretty flat graphs. although I think they had aftermarket head units.
 

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Let’s see a screenshot of what it looks like in the ISA if you don’t mind. Interested to see the difference if any.
 

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Yuck! You have your hands full with only 5 bands of eq. Widen the q and see what you can do. You can set the frequencies too in the parametric eq.
 

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again, probably not necessary. Do you guys think these OEM's just blindly draw a curve to eq their systems? Don't worry too much about the response. Worry about getting full range, and everything in phase. That system has all-pass filters. Take care of those more than anything. From there, worry about volume-dependent low-end roll-off. Also, you are only measuring 40 to 20k. That's why there's nothing below 40. You have to change the measurement settings to measure lower than that.
 

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Discussion Starter · #13 ·
Yeah the other measurement has below 40. Well I figured any oem curve like this would've been put in because it was best for the factory speakers.

I did take measurements for different volume levels, it didn't appear that they did any bass roll off.

I'm not sure what you mean by take care of the factory all pass filters. Do time alignment on my two inputs? or just do the usual time alignment per output?
 

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Yeah the other measurement has below 40. Well I figured any oem curve like this would've been put in because it was best for the factory speakers.

I did take measurements for different volume levels, it didn't appear that they did any bass roll off.

I'm not sure what you mean by take care of the factory all pass filters. Do time alignment on my two inputs? or just do the usual time alignment per output?
Measure with left and right summed. You will see a cancellation in the lower midrange on Toyotas. This is from an all pass filter. It needs to be accounted for via counteracting it with an equal one on the opposite side.
 
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