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      09-20-2009, 07:39 PM   #1
808MGuy
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RTA plots of the OEM Hi-fi system

I just got this PC based RTA setup so I decided to test it out on the OEM system just to see what we're working with. I've always thought the Hi-fi system is pretty decent. Its weakness seem to be over-emphasized midrange, high frequency rolloff and lack of adjustibility. The RTA seems to confirm that.

Here is a reading taken with bass and treble set to flat.




and here is one with some adjustment made on the bass and treble controls



There isn't too much information that can be gathered from these plots partially because the lack of a volume level display on the OEM HU makes it hard to set a reference level. What you have to compare is the differences in peaks in valleys in the plot. Based on my comparison, it appears that the bass control is centered at 100Hz and the treble at 10kHz which is pretty common. The high frequency roll-off is very obvious even with the treble control turned up a bit (I think it was +4 in this reading). Bass is set pretty high (I believe its +8).

My conclusion is that with a bit more adjustment capability like the EQ the premium audio system has, I think you could get this system to sound pretty good. The high end would still be rolled-off but you get a decent sounding system out of this. We'll see what an aftermarket system run off the OEM HU can do once I get it installed.
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      09-21-2009, 08:45 AM   #2
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good stuff

any recommend settings from you to acheive best sound quality?
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      09-21-2009, 09:08 AM   #3
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Nice... it will be very useful as well if you can get an RTA reading at the OEM HU/iDrive outputs without the OEM amp for comparison.
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      09-21-2009, 09:53 AM   #4
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Quote:
Originally Posted by PencilGeek View Post
Did you see the following thread?

Fast forward to post #35.

http://www.m3post.com/forums/showthread.php?t=137825
This is the HiFi RTA, PencilGeek... yours is the Top HiFi RTA.
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      09-21-2009, 10:45 AM   #5
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Quote:
Originally Posted by Technic View Post
Nice... it will be very useful as well if you can get an RTA reading at the OEM HU/iDrive outputs without the OEM amp for comparison.
Hmm. I'm not sure how I would actually get the preamp signal into my laptop and how accurately the sound card in my laptop will be able to receive that signal. I was thinking about using the o-scope feature of the RTA to try to get a clipping point of the HU output but the lack of a volume level display makes that very difficult.
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      09-21-2009, 11:00 AM   #6
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Quote:
Originally Posted by 808MGuy View Post
Hmm. I'm not sure how I would actually get the preamp signal into my laptop and how accurately the sound card in my laptop will be able to receive that signal. I was thinking about using the o-scope feature of the RTA to try to get a clipping point of the HU output but the lack of a volume level display makes that very difficult.
You could tap the OEM HU outputs at the OEM amp connector with these wire to RCA cables http://www.shopatron.com/products/pr...r=91803/1451.0 (you can create your own as well) and use them in your sound card as long as it have RCA inputs and accept balanced signals.
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      09-21-2009, 01:10 PM   #7
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Quote:
Originally Posted by PencilGeek View Post
What were you using for signal generation (source material)?
It is a pink noise track off an IASCA SQ Judging Disc that was used specifically for RTA judging.


Quote:
Originally Posted by Technic View Post
You could tap the OEM HU outputs at the OEM amp connector with these wire to RCA cables http://www.shopatron.com/products/pr...r=91803/1451.0 (you can create your own as well) and use them in your sound card as long as it have RCA inputs and accept balanced signals.
I'm wondering if you would get noise issues that would affect the reading because those adapters use common ground for the L & R signal ground. My laptop sound card is a mini-jack input so those type of connectors are always common ground.
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      09-21-2009, 01:59 PM   #8
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Quote:
Originally Posted by 808MGuy View Post
I'm wondering if you would get noise issues that would affect the reading because those adapters use common ground for the L & R signal ground. My laptop sound card is a mini-jack input so those type of connectors are always common ground.
Those JL Audio cables are straight positive and negative connections to the RCA inner and outer contacts respectively, no common anything.

Just use a wire to mini jack cable from Radio Shack then if your card accepts balanced signals.
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      09-21-2009, 02:12 PM   #9
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Quote:
Originally Posted by Technic View Post
Those JL Audio cables are straight positive and negative connections to the RCA inner and outer contacts respectively, no common anything.

Just use a wire to mini jack cable from Radio Shack then if your card accepts balanced signals.
I'll see if I can come up with something. I'm not sure if the two will be directly comparable since I used an outboard source for the RTA plots I did and the pre-amp plots will be based on a signal generator in the software.
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      09-21-2009, 04:51 PM   #10
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Quote:
Originally Posted by PencilGeek View Post
Why do you need to know if the amps are linear or not? Is it just a curiousity? All you really need to know is the spectrum inside of the car.

I'm guessing your spectrum analyzer has its own microphone that is calibrated to the hardware you're using. Correct?
I guess the curiousity is to see if the preamp signal coming out of the HU is flat. If not, its makes installing aftermarket gear a bit more difficult because you have to undo the internal processing with outboard processors. I was going to use the O-scope feature to find the clipping point of the HU output so I could set gains on the aftermarket amps accordingly but as I said, it is very difficult to do without a volume level display because there's no point of reference.

I'm using the program TrueRTA and a Behringer ECM8000 microphone with the appropriate mic calibration correction file. The microphone is connected to the laptop via a USB Mic Mate so the soundcard in the laptop is bypassed. The Mic Mate has an XLR input on one side and USB on the other.
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