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51
SignalScope Pro / THD measurement
« Last post by geadinc on August 11, 2015, 03:09:33 PM »
I've been asked to optimize a compressor/limiter for a client and I need to check the THD response and minimize it. It's not clear to me that SignalScope Pro would work for me or not. Could someone tell me if it does a reasonable job of measuring THD between input and output of a device?
52
Product Sales & Activation FAQ / Re: Product matrix?
« Last post by KEM on July 09, 2015, 01:21:11 PM »
I would really like to see a product matrix as well for the iOS products in particular.  I want to purchase one or more of the apps, I think, but I was here on the site looking for a matrix to be sure I was selecting the app(s) that best fit my current and potentially future needs without having to email sales/support.

Thanks! - KEM
53
SignalScope Pro / Re: Getting signals into and out of the iPhone and iPod touch
« Last post by bvanl on June 22, 2015, 04:57:21 PM »
I realize this thread seems to be a bit dusty now, but it is still relevant as I've seen others out in the web refer to it.  Since I'm new to the FaberAcoustical products I too found it useful, but have collected additional information which may make interfacing to an iOS device less fuzzy.

Apple Headset Input / Line Output Jack (3.5mm 4 pole TRRS)

None of this is verified other than seeing a schematic for my MacBook Pro and by empirical measurements of both my iPhone5C and MacBook Pro.

Various headset jacks comply with 1 of 2 standards, CTIA or OMTP. 
1. The Cellular Telephone Industries Association (CTIA) or American Headset Jack (AHJ) standard.  This is used by products from HTC, recent products from Sony and Nokia and Apple devices.  Although, Apple accessories use a patented signaling protocol which is likely not compatible with accessories from other manufacturers. 

2. The Open Mobile Telecommunication Products (OMTP) standard.  This is used by most mobile phones, most Samsung SmartPhones and older products from Sony/Ericsson and Nokia. 
However, the OMTP ceased operations and was eventually absorbed by the Groupe Speciale Mobile Association (GSMA) in 2012.

As technology moves forward, it is unknown how long this information will continue to be accurate, or even relevant.

Standard      “CTIA”            “OMTP”
Contact      Signal            Signal
T   Tip      Left Output / HP         Left Output / HP
R   Ring1   Right Output / HP      Right Output / HP
R   Ring2   Ground / Common      Microphone
S   Sleeve   Microphone         Ground / Common
Clearly, differing accessories are not compatible.  Also, Apple products further differentiate themselves by using Apple’s patented signaling.

A simple resistor connected between R2 and S seems to trick my iPhone 5C and my MacBook Pro into thinking an External Mic is attached.  A resistance between 300 and 10,000 ohms seems to do the “trick.”  When this resistance is somewhere above 10K or below 300 ohms, the device will turn off the Mic Bias voltage.  (My iPhone 5C still powered the mic bias with a 12K resistor, and my MacBook Pro turned off the mic bias somewhere around 275 ohms.  I didn’t bother checking further.)

For my particular MacBook Pro (MBP);
There appears to be isolation inductors in the signal paths at the jack.  The series resistance of the one in the Mic signal input path seems to have a nominal 1K ohm resistance and the ones in series with each of the output signal paths appear to have a nominal 220 ohm resistance.  Measurements I made of the output level capabilities of the output driver (open circuit vs a known load) confirm this 220 ohm series resistance.

The “T” tip connector of the device has a switch contact and the “S” sleeve has a separate sense contact.  The sleeve has separate DC and AC circuit paths / functions.

From quickly reading one of many patents and observing the action of my MBP;
The Mic Bias voltage seems to be applied only after a valid accessory has been detected.  The apple device determines when a plug is inserted into the jack by sensing the tip switch.  The apple device also determines if the plug is only a 3 pole (TRS headphone only), or when it is a compatible 4 pole TRRS accessory.

After a plug has been detected, the device applies the Mic Bias voltage which flows through a series 2,200 ohm isolation resistor and the afore mentioned inductor, and then monitors the state of the applied Mic Bias DC voltage.  If the voltage is outside of the design limits, it turns off the Mic Bias voltage.

The device senses the Mic Bias voltage right after the 2,200 ohm series resistor, and this sense path does not include the isolation inductor mentioned above.

The mic audio signal (AC) has 2 or 3 different paths. One is the load of the series bias voltage components (2,200 resistor, plus the afore mentioned inductor) and a 4.7uF bypass capacitor to ground (at the DC bias source).  Another consists of 3 components in parallel to ground (1nF, 15pF, 100,000 ohms).  The remaining path is not completely known, but is the AC coupled input to the ADC.

The Mic Bias voltage is controlled by an IC which is powered by a 3.3V supply and has an I2C bus connection.  Depending upon the DC load of the Mic, or in the case of measuring several different resistances, the expected output of this IC won't seem to be higher than about 2.8 volts or lower than about 2 volts.  This is calculated from actual measurements across external resistances and then applied to internal components as indicated by the schematic of my MBP.  These values may not be entirely precise, but are hopefully less speculative than some of the information I've seen out on the web (not from FaberAcoustical though).
54
SoundMeter / Feature Request to import Mic Cal. Files
« Last post by bvanl on May 26, 2015, 09:35:52 PM »
Please provide the feature to import microphone FRD calibration files.  In app purchase even.
55
IOScope / Re: Feature suggestions
« Last post by FaberAST 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.
56
SoundMeter / Re: Dayton Audio iMM-6 External Mic
« Last post by Bruce on March 12, 2015, 05:16:30 PM »
Hi Ben, appreciate the help...I'll do what you have recommended.

Cheers...Bruce
57
SoundMeter / Re: Dayton Audio iMM-6 External Mic
« Last post by FaberAST on March 12, 2015, 04:27:41 PM »
Bruce,

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.

Ben
58
SoundMeter / Re: Dayton Audio iMM-6 External Mic
« Last post by Bruce on March 12, 2015, 03:53:08 PM »
Hi, the Dayton UMM-6 is a USB device.  I've purchased the Dayton Audio iMM-6, this microphone connects via the TRRS headphone jack.  Some apps such as Studio Six Digital import the calibration file provided by Dayton Audio.  I though the Faber app may have provided similar functionality.

The following link from Dayton shows the procedure for the Studio Six app.
http://www.daytonaudio.com/index.php/imm-6-idevice-calibrated-measurement-microphone.html

Cheers...Bruce
59
SoundMeter / Re: Dayton Audio iMM-6 External Mic
« Last post by FaberAST on March 12, 2015, 10:40:03 AM »
Bruce,

Here's an excerpt from a recent blog post regarding SoundMeter's hardware support:
Quote
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.
60
SoundMeter / Dayton Audio iMM-6 External Mic
« Last post by Bruce on March 11, 2015, 11:45:42 PM »
Hi, is it possible to calibrate a Dayton iMM-6 to an iPhone 4 running SoundMeter 7.0.1.  Any assistance would be very much appreciated.

Cheers...Bruce
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