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Thread: true rta spl meter program

  1. #1
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    true rta spl meter program

    i recently downloaded this program and having got good readings.
    in competition i hit 143 db spl and when i use this program on my lab top i only hit 120's i am only using the built in mic on computer.

    does any one know what equipment u need to get good readings from this program? OR DOES ANYONE have this program and works good for them?

    send any info to [email protected] thanx

  2. #2
    MySQL Error scott_fx's Avatar
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    i'd say it's your mic
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  3. #3
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    I figure you're talking about this app?

    http://www.trueaudio.com/

    Are you using the free version? Did you do any calibration?
    :: Mark

  4. #4
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    yes the free version no i did not calibrate im new at this i just buy and install dont no the tecnicalitys my stero rips though just want to be able to meter it on my own so i can tweak it more currently hit 143 not bad for begginer

  5. #5
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    Quote Originally Posted by scott_fx View Post
    i'd say it's your mic
    do i need a mic mixer or those special mics for lab tops

  6. #6
    Constant Bitrate pate60's Avatar
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    Q: Besides TrueRTA, what else do I need to set up my own audio test lab?


    A digital voltmeter to calibrate TrueRTA™ for your sound card
    A collection of cables and adapters for connecting electronic gear to your sound card for testing. Most sound card jacks are 1/8 inch

    If you want to do acoustic testing of loudspeakers in addition to the above you will need:
    A calibrated microphone
    A microphone preamplifier or mixer
    An audio power amplifier to drive the speaker under test
    Cables to connect the line out of the sound card to the input of the audio power amp

  7. #7
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    Quote Originally Posted by kiaz69 View Post
    yes the free version no i did not calibrate im new at this i just buy and install dont no the tecnicalitys my stero rips though just want to be able to meter it on my own so i can tweak it more currently hit 143 not bad for begginer
    Wow... ummm, the lack of calibration is a HUGE issue. Here's a crash course in what a "decibel" is and how it gets measured.

    A "decibel" is a couple of different things, and can be confusing to measure. There are also a number of scales used to measure decibels which adds to the confusion.

    A decibel can be an _electrical_ measurement (dBv, dBm), or a _pressure_ measurement (dB). What you're looking for is the pressure measurement... In order to measure this, you'll use the microphone in the laptop which will need to be "tuned" in the car at a specific physical location at a specific frequency. If you don't do this, then the program is only reading a voltage from the microphone input and "plotting" it again some internal scale. I will guarantee that TrueRTA will not be accurate out of the box - since it knows nothing about the acoustical environment that you're using it in, nor about the response characteristics of the microphone, mic amp (in the laptop), etc.

    From what I see on the website, it looks like the free version of TrueRTA comes with "Microphone Calibration Files" which I would figure to mean that it can calibrate itself in a specific environment. You need to do this.

    The process will usually entail having your laptop playback a file while the microphone listens. The file will probably be a "sweep", and will have been recorded at a known level (this is the electrical dBv). You'll be instructed to manipulate the level of the playback system to a certain point, then the level of the mic input on the laptop. Once that TrueRTA can "hear" the whole file, you'll probably be walked through setting levels for "0 dBa". This is the calibration point, you're teaching TrueRTA to recognize what it "looks like" when the SPL in the car is 0 dB.

    Once this is done, you're pretty much ready to go.


    To test the dB level in the car _as was tested at dB drags_ you'll need to know the "weighting" that the measurement was done on; and you'll need the file/audio clip they used to take the measurement. Both of these are very important if you're looking to match the numbers you got at the dB drags.

    Once you have all this lined up, you should be able to test and get the same numbers you got at the drags. MIC PLACEMENT WILL BE VERY IMPORTANT. If they clamped a mic to a headrest, you can't expect to get the same numbers with a laptop on the seat.


    NOTE: It is VERY VERY important that you not be in the vehicle when you're taking the measurements!!! You could easily blow an eardrum at the levels you're talking about!


    ref:
    http://www.phys.unsw.edu.au/~jw/dB.html
    http://en.wikipedia.org/wiki/Decibel
    :: Mark

  8. #8
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    kiaz69;

    I wanted to answer your PM in public 'cause I think it's worthwhile for the archives and other people on the thread. I hope you don't mind...


    Quote Originally Posted by kiaz69
    do u know lots about this program if so please help me if its worth running this program
    Hey man...

    Specifically, I don't know anything about TrueRTA.... I have a lot of experience in setting up rooms and using RTAs, but I'd never seen this app before today.

    Personally, I think it's overkill for what you're trying to do - that being just get an idea of the SPL in your car to (presumably) increase it in order to to better at the next dB drags.

    If so, then I would NOT spend time with this app... you would do just as well dropping $50 on a simple dB meter from Radio Shack:

    http://www.radioshack.com/product/in...ductId=2103667
    http://www.radioshack.com/product/in...ductId=2103668

    Those would be a LOT easier for you to deal with. Basically you turn it on, start a CD playback, grab your remote volume control and get out of the car.
    :: Mark

  9. #9
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    I have one of these......

    http://www.termpro.com/storefront/

    www.termlab.com


    Thats what you need.

    Tiny

  10. #10
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    Quote Originally Posted by kiaz69 View Post
    currently hit 143 not bad for begginer
    If you're planning on competing, there are beginners that will walk all over this, even in the lowest of classes.

    I would recomend spending some money on a mic, and read the manual on how to calibrate the software. Otherwise, you're just shooting in the dark.
    Jan Bennett
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    Please post on the forums! Chances are, someone else has or will have the same questions as you!

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