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Thread: REW and DSP help - Acoustical vs Electrical crossover.

  1. Back To Top    #11
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by DirtyBumOAK510 View Post
    So I just realized I've been living in bonehead land. Somewhere I could have sworn I read that you should EQ with Sine sweeps and not pink noise. So thats how I eq'd my last build. Now I'm halfway through EQing this one and realizing the error of my ways after chatting with someone. So I'm supposed to have been using periodic pink noise. After searching the forums, this has become clear. Doh!

    So my questions of the day, which I ask after scouring threads all afternoon and still not feeling confident.

    1. When do we use sine sweeps? What purpose do they serve?
    You can set your frequency response using sine wave sweeps (chirps) or pink noise. Either method works good. When using REW, I find it's a little easier to wave the mic around for a while to get a spatial average while using pink noise, compared to making multiple sweeps in multiple locations and then averaging a bunch of traces in the program. However, chirps can give you polarity and phase information which pink noise cannot, so I find chirps useful for sanity fhecking the polarity and setting the time delays.

    Quote Originally Posted by DirtyBumOAK510 View Post
    2. I'm setting my EQ by using 8 measurements, (Left speaker = 3 left ear, 5 right, Right speaker = 2 left ear, 6 right ear), then taking an average. Then plotting that against my custom house curve (Andy's bass, Jazzis dip (verified by Eric Stevens)) So if I'm using periodic pink noise... How long do I need to take each measurement (per ear)? It seems link pink noise repeats itself every 3.5 seconds, so is that as long as I need to take a measurement?
    What do you mean by "verified by Eric Stevens"?
    Also, you're right that periodic pink noise is a repeating pattern. That is the "periodic" part. If you have the FFT size of the RTA set the same as the sequence length of the pink noise, and if you have the window on the RTA set to "none" or "rectangular" then to get the RTA result fully updated you only need to measure for a cycle or two of the pink noise which is around a second or two. If you are doing a spatial average to capture near your left ear, right ear, and so on ... then you'll want to ensure the "averaging" feature is set to infinite and capture a cycle or two of noise at each location. So if you're waving the mic around near your left ear, we could consider that 3-5 locations and you'll want something like 5 seconds of capturing in that area. Then another 5'ish seconds near your right ear.

    The exact amount of time is not critical. The important thing is can you make the measurements reapeatable? Like if you make a "measurement" using whatever method you want, can you make a second (separate) measurement and then compare the traces and have them agree really nicely? That is when you know you're moving slow enough, measuring for long enough, and doing it "right".

    Quote Originally Posted by DirtyBumOAK510 View Post
    3. When downloading Periodic pink noise ... I know that I match the FFT on my RTA graph. But when downloading the periodic pink noise, I'm downloading it at 0dbfs? Left only? (for left speakers) and vice versa R only for right speakers? Because L+R pink noise is no longer mono ...

    Thanks in advance.
    Pink noise should be 0dBFS meaning the loudest momentary peaks in the noise file should be at maximum level (in the recording). You'll want to also pay attention to the crest factor which is the difference between the loudest peaks and the average energy. Aim for a crest factor of 12dB if you can, and REW should let you choose this number. If you set the crest factor to a really small number in REW then it will start sounding very distorted and likely not give you a good measurement.
    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)
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  2. Back To Top    #12

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by Justin Zazzi View Post
    What do you mean by "verified by Eric Stevens"?

    If you are doing a spatial average to capture near your left ear, right ear, and so on ... then you'll want to ensure the "averaging" feature is set to infinite and capture a cycle or two of noise at each location.

    You'll want to also pay attention to the crest factor which is the difference between the loudest peaks and the average energy. .
    Re: "Eric Stevens Verified". Verified wasn't the appropriate word. I asked him what his preferred house curve was and he told me the same dip in the ~1.5khz-5khz region. I believe he even used the same exact numbers that your text file uses.

    Averaging to "Infinite" is Averaging "Forever"? That is how REW words it.

    Where are you finding the "Crest factor"? Is it that "2.15dbfs peak"? I googled it and it popped up that you can change it to "CTA-2034" to increase that number to ~9. But I'm not exactly sure what that will do. I'm not sure what CTA-2034 is or if it will affect the "Full range".
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    Last edited by DirtyBumOAK510; 08-27-2020 at 11:06 PM.

  3. Back To Top    #13
    Noob Jdunk54nl's Avatar
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    Re: REW and DSP help - Acoustical vs Electrical crossover.

    You don’t want your generator digitally clipping (the red on the wave form and your peak is +2.15 dbfs. That is not going to be good. The peaks should never exceed 0dbfs
    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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    Noob Jdunk54nl's Avatar
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    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Also, I just found this out thanks to Justin, if you double click on the image after uploading, you can adjust size of them. That way people can see them without having to click on them
    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

  5. Back To Top    #15

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    So how do I change it?
    I'm a bit confused now. I want that big number to be 0, and the small number to be +12? or -12?
    I'll post some shots of some of the options I have.
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  6. Back To Top    #16
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Sorry I'm not on the Beta branch of REW so my thoughts above will be misleading.

    I read the beta documentation and it looks like you're doing everything right but the big number should read "-6.00dBFS" or smaller, as in more negative like "-12.00dBFS". That number sets the RMS or average number and works different than I thought it did. Oops!

    Make sure you remember what the sequence length is. Your screenshot shows 64k. I like to put it in the filename of the wav file so I never forget it. You'll need that number when you set the FFT length in the RTA module. If you use a alittle shorter length like 32k or 16k then it will repeat itself faster which means the RTA will update faster.

    If you'd like to create a wav file and share it, I can analyze it to make sure it works the way we think it does.
    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.

  7. Back To Top    #17

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by Justin Zazzi View Post
    I read the beta documentation and it looks like you're doing everything right but the big number should read "-6.00dBFS" or smaller, as in more negative like "-12.00dBFS". That number sets the RMS or average number and works different than I thought it did. Oops!

    If you'd like to create a wav file and share it, I can analyze it to make sure it works the way we think it does.
    Hmmmm .... CAJ won't let me upload wav files. Email? What is the preferred method for sharing wavs here?
    Thank you for the help. I can share 2 files. One has the big number as -12, the other has the small number as -12. I'm assuming its the small number is the "crest". Both files avoid clipping.

    Am I right in assuming that I use a "Left Channel" to tune my Left speakers, and a "Right Channel" to tune my Right speakers? What about if I want to match levels between left and right? For instance if I'm trying to match my midbass to my horns?

    Cheers.

    Progress!

  8. Back To Top    #18
    Noob Jdunk54nl's Avatar
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    Re: REW and DSP help - Acoustical vs Electrical crossover.

    This is the file I use of Pink PN 64k
    This was generated with REW and is about 11 minutes long. This was generated with -12dbfs for the file and peaks are like -9dbfs.

    https://drive.google.com/file/d/1c5w...ew?usp=sharing
    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

  9. Back To Top    #19

    Re: REW and DSP help - Acoustical vs Electrical crossover.

    Quote Originally Posted by Jdunk54nl View Post
    is about 11 minutes long. This was generated with -12dbfs for the file and peaks are like -9dbfs.
    Looks similar to what REW wants to produce for me. -12dbfs exactly and a "-9.85 dbfs pk"

  10. Back To Top    #20
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: REW and DSP help - Acoustical vs Electrical crossover.

    My favorite tool to use is ACX Check plugin for Audacity since it's free and calculates a bunch of stuff for you. I recommend you give it a try and see if it works for you. It doesn't work for me for some reason. Instead, below is a Matlab script for doing something similar. The results are at the bottom. There is an open-source version called Octave that everyone can download and use if you'd like to give it a try. You can analyze your own files using the code below.


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    Looks like the peak value is -9.75dBFS which matches what you saw. The crest factor is close to 6dB which matches the documentation from the REW Beta help files. But the average value is -15dBFS which doesn't match what you saw on the screen. I'm not sure why that is.
    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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