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Messages - FaberAST

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Bluetooth mic input is typically sampled at 8 kHz. The weighting filters in the Meter and the bandpass filters in the Octave analyzer are designed to operate at multiples of 44.1 kHz and 48 kHz, which would explain the "Unsupported Sample Rate" message.

It seems that some time ago Apple changed the behavior of Bluetooth audio in iOS (at least in the Measurement Mode that SoundMeter uses). Since SoundMeter requires both input and output from the audio system, Bluetooth won't work unless you are using a Bluetooth headset (or hearing aids, in your case) with both input and output. Unfortunately, if you use a headset for input and output, then the sample rate will be restricted to 8 kHz (for both input and output).

This is a change from how Bluetooth used to work on iOS, when it was possible to use the built-in mic with Bluetooth output.

I wish I had better news.



I'm not aware of any affordable sound level meter software for Windows.

You might consider an iPod touch as a less expensive alternative to the iPhone. The accuracy of your measurements will depend on the quality of your calibration, regardless of which device you use. You can get more reliable measurements with an external measurement microphone, like the MicW i436.


SoundMeter / Re: Using Exteral Microphones and Calibration
« on: January 25, 2016, 10:27:37 AM »
SoundMeter's built-in documentation includes a device input voltage calibration tutorial.

To access the documentation, tap the info button ("i") in the toolbar at the top of the main screen. Then, tap on Help in the Info screen.

Electroacoustics Toolbox / Re: nan dB
« on: October 26, 2015, 08:26:51 PM »
"nan" stands for "not a number" and indicates that some invalid arithmetic operation occurred (like dividing zero by zero).

SignalScope Pro / Re: THD measurement
« on: October 16, 2015, 01:43:00 PM »
Am I correct in assuming that the number of spectral lines is equivalent to the number of bins?
Yes. Each line represents one bin.

SignalScope Pro / Re: THD measurement
« on: August 13, 2015, 10:24:41 AM »
SignalScope Pro's FFT Analyzer tool is capable of computing THD with up to 15 harmonics.
In order to get good results, you'll need to use a test signal that's at a frequency that matches one of the frequency bins in the FFT. This is fairly simple if you use SignalScope Pro's built-in signal generator and use the same audio device for both output and input in your measurements.

IOScope / Re: Feature suggestions
« on: March 16, 2015, 10:26:13 AM »
IOScope 5 added frequency smoothing in 1/6th, 1/12th, and 1/24th octave band resolution. It also added support for loading previously captured measurements for direct comparison with the live curve.

SoundMeter / Re: Dayton Audio iMM-6 External Mic
« on: March 12, 2015, 04:27:41 PM »

I'm sorry, I obviously misread your post.

Are you looking for frequency response compensation (FRC) or sensitivity calibration? If you are looking for FRC, it is not supported in SoundMeter. FRC only works with FFT-based spectrum analysis.

If you are looking for sensitivity calibration, then you would need to enter the iMM-6's acoustic pressure sensitivity in the Input Channels calibration screen (there is calibration tutorial information in SoundMeter's built-in documentation).

The iMM-6's calibration file includes the mic's overall sensitivity on the first line. (You can download the file directly at http://www.daytonaudio.com/iMM6_Lookup_Tool/iMM_Text/99-00192.txt, where you replace "00-00192" with your own mic's serial number.)

The nominal sensitivity for the iMM-6, given by Dayton, is -40 dB, where 0 dB = 1V/Pa. To convert that to V/Pa (to enter into SoundMeter), you need to raise 10 to the power of the sensitivity divided by 20. That is, 10^(-40/20) = 0.01 or 10 mV/Pa (which Dayton also gives as a nominal sensitivity). The sample file they provide has a sensitivity of -37.4 dB, which equates to a sensitivity of 10^(-37.4/20) = 13.49 mV/Pa, which you could enter into SoundMeter either as "13.49m" or "0.01349" (SoundMeter can recognize the "m" and format the number appropriately).

Keep in mind that you need to have the headset input device units set to "V" and the headset input channel units set to "Pa" in order for this to work. Also, you'll still have a nominal calibration. If you need a more accurate calibration, I would recommend performing a relative calibration against another sound level meter that you know has been accurately and properly calibrated. (I recommend this, regardless of which or whose iOS sound level meter app you are working with.)

Please let me know if you have questions about any of this.


SoundMeter / Re: Dayton Audio iMM-6 External Mic
« on: March 12, 2015, 10:40:03 AM »

Here's an excerpt from a recent blog post regarding SoundMeter's hardware support:
The new SoundMeter apps also support the Dayton UMM-6 USB measurement microphone. When the UMM-6 is detected, the user will be prompted to enter its serial number, which is typically printed on a label on the UMM-6. If a valid serial number is entered, SoundMeter will automatically download a calibration file from Dayton’s website and set the microphone sensitivity based on the information in the file.

Note: The Dayton UMM-6 must be connected to your iOS device via Apple’s USB camera adapter (either for Lightning or 30-pin dock connector, depending on your device). Sometimes the UMM-6 shows up in iOS as USB PnP Sound Device. If that happens, unplugging the UMM-6 and plugging it back in will generally solve the problem (it may take 2 or 3 tries). When properly connected, “UMM-6″ will appear as the input device name in SoundMeter’s toolbar (at the top of the screen).

This should work the same on any iOS device that runs the current version of SoundMeter.

Please let us know if you have other questions.

SoundMeter / Re: Calibration - micW i436
« on: November 19, 2014, 09:09:57 AM »
For the i436, you can follow these instructions. This assumes that the sensitivity of your i436 is 6.7 mV/Pa. You should substitute the factory-calibrated sensitivity that you received with your i436.

Launch SoundMeter.
Plug in the i436.
Tap the gear button in the toolbar at the top of the main screen in SoundMeter.
Then, tap on I/O Device Configuration to find the Input Options menu.
Make sure the Input Device is "Headset Microphone".
Make sure Device Units is set to "V".
Then, tap on Input Channels and make sure that All Channels units is set to "Pa".
Under CH1, tap Calibrate, and in the Input Sensitivity text box you can enter "6.7m" or "0.0067" to make sure that your input sensitivity is set to 6.7 mV/Pa.
If the Input Sensitivity text box shows units other than mV/Pa, then you must have missed one of the earlier steps.

RoomScope / Re: Interrupted Pink Noise
« on: March 31, 2014, 10:26:55 AM »
The interrupted noise method is not currently supported, although it may be added as an option in a future update.

SoundMeter / Re: Data Logging
« on: March 27, 2014, 02:05:42 PM »
Data logging is coming within the next few weeks...


Are you referring to the tutorial on the blog (http://blog.faberacoustical.com/2013/mac/frequency-response-measurement-with-signalscope-pro-3-mac/)?

Every time I try to follow the instructions the FFT only shows me what is happening at that precise moment, not the full result of the frequency sweep from 20 Hz to 20 KHz.
If you follow the tutorial, you will have the sweep set to repeat. You will also have the sweep length configured to match the FFT. If either of these is not configured as indicated in the tutorial, then you won't see a stable frequency response magnitude trace in the FFT analyzer. Additionally, the FFT analyzer will need to be using a Uniform (rectangular) data window.

Frequency response measurements are much easier, more reliable, and more precise when you use the Dual FFT Analyzer tool in Electroacoustics Toolbox. The Dual FFT tool will also give you phase, group delay, coherence, impulse response, and cross-correlation data.


Electroacoustics Toolbox / Re: Room Analyzer - best practice?
« on: February 07, 2014, 05:28:43 PM »
I'm not sure I know what you mean by "waiting for the analysis to complete (and stop on its own). Once I start the Dual FFT, it just runs. The excitation signal continues until I stop the tool. I did let it run for two minutes before stopping it. Should I wait longer? Seems like 10 repeats should happen much more quickly.

At which point do I click on "Capture Data?" While the excitation is running? After I stop the tool? I've tried both and I'm just getting an empty graph.

If you set the averaging type to Linear, the measurement will stop after the specified number of averages has been reached. I would recommend capturing the data after that.

Your screenshots clearly indicate that you are not yet getting valid measurements within the DFFT Analyzer, so that issue needs to be resolved before worrying about bad results from the Room Analyzer.


Electroacoustics Toolbox / Re: Room Analyzer - best practice?
« on: February 06, 2014, 10:57:18 AM »

Next created a Dual FFT Analyzer. In the bottom drawer I set the source to the appropriate Apollo 16 input. Under the "Excitation" tab, I Selected the appropriate output channel...sine sweep...Logarithmic. I left all other settings at default.
Did you select the same (excitation) output channel for the Reference input (next to the Source input selection)?

Next I selected Control->Start All Tools. I confirmed that I could hear the repeating excitation signal in the room and that the mic was picking it up. While the excitation signal was in progress, I selected Control->Capture all Data. Then I stopped all tools.
If you have any other tools in your project, I would recommend just starting and stopping the DFFT Analyzer directly, rather than all tools simultaneously. Also, for room measurements, you might want to set the averaging type to Linear and let the analysis complete (and stop on its own) before you capture the data. (The default number of averages, 10, may be overkill, but it won't hurt your measurement.)

Also, before capturing the data in the DFFT Analyzer, I would recommend that you inspect your measurement data to be sure it looks right. If you are familiar with ETC or squared impulse response curves, I would recommend that you select the Squared IR function in the Display tab and make sure you see the kind of acoustic decay you would expect in your measurement. If you don't have valid measurement data in the DFFT Analyzer, you can't expect to get meaningful results when you load it into the Room Analyzer.

The Coherence function can also be used to verify the quality of your measurement, as a function of frequency. A coherence of 1 is ideal. The smaller the coherence, the less meaningful your data is at a particular frequency.


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