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Author Topic: Smaart v7 SPL meter.  (Read 2960 times)

Al Rettich

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Smaart v7 SPL meter.
« on: August 29, 2016, 10:49:39 pm »

It's been so very long since I've been asked to set up the SPL section of the Smaart wondering if anyone had a true "proper" way of doing it?
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Mark Oakley

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Re: Smaart v7 SPL meter.
« Reply #1 on: August 30, 2016, 12:45:02 pm »

I use mine all the time. I'm on SMAART 7.5.2.

First, click on the small downward-facing triangle on the top right corner of the SPL display and select which channel on your interface the measurement mic is on. Be sure that the dbA SPL slow setting is selected on the lower left triangle of the SPL window.

Next, click on the large white numbers (the SPL value) and that will open up the Sound Level Options. I use a cheap level 2 calibrator that I bought from ebay: http://www.ebay.com/itm/SC-05-Industrial-Sound-Level-Meter-Mic-Calibrator-94-114-dB-IEC-942-Class-2-NEW-/190673886600?hash=item2c650c9d88:m:mpDuuSBnMJhGk94nsXW_NHQ  with my pair of RTA 420 mics. It's important that the mics have an airtight fit into the calibrator, so I put a small piece of clear tubing over the body of the mic near (but not at) the diaphragm end so it would fit tightly into the calibrator. Turn the calibrator on- I usually use the 94 db setting. If your RTA is running you should see a large spike at 1k.

In the Sound Level Options window, click on the Calibrate tab, which will open up the Amplitude Calibration window. Hitting the Calibrate button will start the calibration process, and a progress bar will open up and run.

Once the progress bar is done, hit OK and Apply, and the SPL meter should show 94 db. It's important not to adjust the gain knob for that mic on your interface after that.  Also this process works better in the absence of background noise-don't try this when the band is playing.

When running the SPL meter, I usually use the dbA LEQ setting with a time window of about 4 minutes, which corresponds to the average song length.

-Mark
« Last Edit: August 31, 2016, 09:43:47 am by Mark Oakley »
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Mark Wilkinson

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Re: Smaart v7 SPL meter.
« Reply #2 on: August 30, 2016, 03:09:23 pm »

Ditto to what Mark said, other than my monitoring preference is spl flat or C-weighted...pure preference....

One thing I would add if you are using multiple mics is to pay close attention to the manual's calibration instructions.

I didn't, and kept finding the SPL meters would read the same across all the mics I calibrated, but at the same time the RTAs would show different levels.

The reason is that Smaart will set the mic to 94db with whatever I/O device channel gain, that's being used.
However, the I/O device's actual output is measured as dBFS, and determines the relative levels of RTA and transfer traces.

So what I do is set dBFS first, prior to calibration.
Toggle the meter to dBFS. Turn the mic calibrator on, and dial the I/O device gain to a particular chosen dBFS.  (I use -20dBFS for a variety of reasons.)
Then run calibrate in smaart.  Now the mic will read 94db, and when you toggle the meter to dBFS, it will read -20.
Do this for all your mics on each of their I/O channels, and then all RTA and transfer traces will show the same level given the same stimulus....otherwise they won't!!

It's also important to set dBFS prior to calibration if your mic is in danger of running out of SPL measuring room...the little red clip light in the meter will let you know a bad...
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Mark Oakley

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Re: Smaart v7 SPL meter.
« Reply #3 on: August 30, 2016, 09:02:19 pm »

Hey Mark-are you using SMAART v8?

-Mark
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Mark Wilkinson

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Re: Smaart v7 SPL meter.
« Reply #4 on: August 31, 2016, 08:16:28 am »

Hi Mark, yes v8 mostly, although I have v7 on an older laptop.

I was checking what I suggested above on the v7 laptop and noticed one difference vs v8......

The little red/green status indicator in SPL mode stays green in v8 until clipped .... whereas it just says red in v7  (green when LEQ working)

I also found out trying to run SPL into clipping, that the most a UMC404 I/O can put out as a soundcard is -10dBFS, so my advice about watching for red light 'bad' is device specific, and somewhat bogus...
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Chris Tsanjoures

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Re: Smaart v7 SPL meter.
« Reply #5 on: August 31, 2016, 11:44:56 am »

The 'clip' indication does not necessarily refer to your mic clipping, but the internal mechanism in the analyzer.

For example, if you calibrate the SPL meter to 94db, at -10 dB FS in Smaart, you only have the ability to measure up to 104 dB SPL before the analyzer clips. Though, your microphone/preamp combo may still have plenty of headroom.

So, you are absolutely correct. It is largely specific to the gear you have/how loud the program is/how much gain is on the preamp of the mic input.
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Dave Garoutte

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Re: Smaart v7 SPL meter.
« Reply #6 on: November 02, 2016, 04:35:25 pm »

I came up with a cheapo method that isn't particularly accurate, but gets me some numbers.
I run PA pink noise up to 94db on my phone ap, when held right at the measurement mic.
Then I run the calibration routine (Smaart v8).
It actually works pretty consistently and gives me something to work with.
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Ivan Beaver

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Re: Smaart v7 SPL meter.
« Reply #7 on: November 02, 2016, 08:30:19 pm »

I came up with a cheapo method that isn't particularly accurate, but gets me some numbers.
I run PA pink noise up to 94db on my phone ap, when held right at the measurement mic.
Then I run the calibration routine (Smaart v8).
It actually works pretty consistently and gives me something to work with.
That is assuming your phone is accurate.

I have seen them be off a bit.

But it is probably "close enough for Jazz".
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Nicholas C. Ames

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Re: Smaart v7 SPL meter.
« Reply #8 on: November 03, 2016, 01:25:26 am »

Forgive me if this is a stupid question, but with regards as to whether or not to use A or C weighting, isn't the point of using a 1kHz tone in a mic calibrator so that it wouldn't matter what weighting was applied. If you overlay A C and Z weighting curves, they are all 0dB at 1kHz. Therefore, even if your meter in Smaart was set to A when you ran the calibration routine, you could still switch to C or Z (unweighted) and the results would still be accurately calibrated. Using any kind of broadband noise however, during the calibration routine, or any single tone OTHER than 1kHz would be dependent on the weighting setting for accuracy. Yes? No? I'm not an old pro at this stuff like a lot of you guys, but recently I THINK I realized that I was fretting over the weighting used during calibration (not necessarily with Smaart specifically, but still the concept applies) until I realized that A,C and Z weighting are ALL 0dB at 1kHz.

Please correct me if I'm way off base here, learning about this stuff is a serious passion of mine, it's far more than just a job to me. :) as always, I'd like to extend a big thank you to all who share knowledge on this forum and others!
« Last Edit: November 03, 2016, 01:27:38 am by Nicholas C. Ames »
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Mark Wilkinson

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Re: Smaart v7 SPL meter.
« Reply #9 on: November 03, 2016, 02:49:24 pm »

Forgive me if this is a stupid question, but with regards as to whether or not to use A or C weighting, isn't the point of using a 1kHz tone in a mic calibrator so that it wouldn't matter what weighting was applied.

Your understanding matches mine.
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