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Thread: Is it possible to use REW to measure RCA outpu

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    Senior Member Smitty's Avatar
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    Is it possible to use REW to measure RCA outpu

    Like the title says, can use REW to measure the response of an RCA output signal?
    Meh, it'll play.

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    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    Absolutely.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

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    Senior Member Smitty's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    . You did answer the question I asked. Care to elaborate? RCA to 3.5mm plug?
    Meh, it'll play.

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    Senior Member Smitty's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    I guess I could brush on my Google skills.
    Meh, it'll play.

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    Re: Is it possible to use REW to measure RCA outpu

    You can do it through a headphone in... but far better to use a decent audio interface that doubles as a mic interface

    i use a Scarlett focusrite 2i2 and each input can be made to analyse a line level signal

    set it as the input with pink noise playing and hit rta like normal ie it’s no different from using a mic as an input, a mic turns air movement into electrical... the rca signal starts as electrical ����

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    Senior Member Smitty's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    Thank you. After I was done laughing at Jazzi's response, I checked out some videos and posts. That unit or similar was mentioned/used.

    In this case, I don't need high end. I only want to get a basic look at the OEM eq, see if the bass rolls off with volume, and find where it starts clipping. I'd prefer to spend the money on a new head unit eventually.

    This RTA measurement was done on the same vehicle but a newer year. The radio has been updated but, I imagine the eq is similar since the speakers have been the same for years. If I read it correctly, it's a 21.5db swing. That curve is very similar to what I've been fighting. In his vehicle, the bass doesn't seem to roll off with volume.

    It is clear, the best solution is a new head unit but that's going to be a while.

    I have considered a unit that will knock the peaks off of that signal then use my dsp to process a flatter curve but, that's a bandaid and seems counterproductive.
    Meh, it'll play.

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    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    Quote Originally Posted by Smitty View Post
    . You did answer the question I asked. Care to elaborate? RCA to 3.5mm plug?
    Sorry, couldn't help it!

    But yeah, like dumdum mentions you can just play pink noise and then "measure" it using the line input on some sound card you have. Just be careful about the voltage you try to measure. Anything over ~2vrms starts getting sketchy for sound card inputs like this. You can knock down the voltage using a line-output-converter or by building a voltage divider with some resistors.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

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    Senior Member Smitty's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    Thank you. I was thinking I could set the dsp to flat and limit the dsp volume to 2v instead of trying the measure the speaker output. I just wanted to make sure there wasn't something I was over looking. Sometimes my ideas can go sideways on me.
    Meh, it'll play.

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    Noob Jdunk54nl's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    I outlined the parts I used here: https://www.f150forum.com/f30/head-u...3/#post6488321

    I just used all of this to get a nice loopback for about $20 in cost at the time. I used the external usb sound card so I didn't fry my computer. I've done that before, now I try to use external if I am connecting something that could potentially send too much in.

    I output the sound from the computer and played a sweep with REW. It then went into the HU and out to my RCA attenuator (to lower the level to less than 1v) which then went back into the usb sound card.

    Note: Everytime you adjust the level of the attenuator, make sure to calibrate the sound card loop (without HU) in REW. That attenuator does not change the frequency equally when adjusted.
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

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    Senior Member Smitty's Avatar
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    Re: Is it possible to use REW to measure RCA outpu

    Quote Originally Posted by Jdunk54nl View Post
    I used the external usb sound card so I didn't fry my computer. I've done that before, now I try to use external if I am connecting something that could potentially send too much.
    Sooo, you're saying I could possibly also get a new motherboard out of this?

    All jokes aside, thank you. That should get me the little bit of info I'm looking for.
    Meh, it'll play.

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