12. April 2016

Directivity of Microphones in Portable Devices

Directivity of Microphones in Portable Devices
Portable devices such as smartphones, tablets or laptops are often used in hands-free mode for telephone calls. For the manufacturer of the device, it is important to ensure that the microphone is able to pick up the speech from all directions so that the user is well understood. With the new version of the microphone test software RT-MicFX, NTi Audio offers a simple and convenient method to determine this microphone directivity.

Portable devices are used extensively in our daily verbal communication, and more and more communications applications are being launched. Often, such portable devices are utilized in a hands-free mode; the device stays in one place, and the user moves freely in space. This presents a challenge - the intelligibility of the speech should remain clear and consistent, regardless of the talker’s position. Some devices employ more than one microphone to increase the number of positions from which speech can be detected and thereby improve the quality of the spoken message.

From the perspective of the testing engineer, measuring a microphone in such an environment may seem formidable because the signal received by the microphone generally cannot be forwarded in real time to an audio measurement system. With the NTi Audio microphone test system this task is made very easy. The device to be tested is placed on a turntable. This is located in front of a sound source. The measurement is carried out in two sequential steps:

a) First, the device under test (DUT) is gradually rotated 360 degrees. At predefined angles, a sound is played to indicate that the test signal is about to start. This trigger signal is required in step 2. A gliding sweep test signal is then played towards the DUT. All signals received by the microphone are continuously recorded, for example, with a voice recorder app within the device.

Microphone Polar Pattern

b) In the second step, the headphone jack of the DUT is connected to the FX100 Audio Analyzer and the recorded sequence of test signals are replayed. The measuring system automatically recognizes the trigger signal, analyzes the test signal that follows and creates a polar diagram of the microphone.

Microphone Polar Pattern

Both the turntable and the FX100 Audio Analyzer are driven by the RT-MicFX PC-software. The polar diagrams can be customized through the choice of frequencies, color, degree of smoothing and interpolation.

The RT-MicFX Software 2.70.0 version is available as a free update to all owners of RT-MicFX software at the NTi Audio Support website.

More information about microphone testing.

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