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Frequency Response with P50 Speech

Introduction

Modern audio devices such as cell phones, headsets, and VoIP phones often contain a significant amount of on-board processing. This makes it challenging to test them with traditional methods such as sine-based stimuli. It is becoming increasingly desirable and even necessary to use stimulus signals that present the device under test with a waveform that is more representative of real-life use such as real or artificial speech signals.

This sequence demonstrates how to measure the frequency response of a device using P50 artificial speech as the stimulus signal. One of the challenges of using a speech-based signal is that it does not have a flat frequency characteristic. Because of this, the test must compensate for the response of the stimulus in order to isolate solely the frequency response of the device under test.

This sequence uses the RTA analysis option in SoundCheck, specifically the frequency response output (a new feature which was introduced in SoundCheck 10.1). The test begins with an option to recall stored data from disk. If the user chooses not to recall data they will be prompted for a desired test level in Vrms. The P50 stimulus is then played through the DUT and recorded by a reference microphone or ear simulator. The RTA spectra of the stimulus and the response waveforms are both calculated, as well as the overall frequency response. All three curves are displayed on two graphs.

 

Final display for Frequency Response with P50 Speech sequence

Required Equipment

Hardware

• No specific requirements - depends on device under test

Software

• SoundCheck 10.1 or later
• Stimulus Editor Listen p/n 2017
• RTA option Listen p/n 2005

 

System diagram

*Please note that this diagram is showing a simple test setup for a loudspeaker. This test sequence is non-application specific and could be used for a number of devices including headsets, cell phones, VoIP phones, and more. If you need assistance adapting the sequence to your specific application please contact us.

Hardware Setup & Calibration

1. Calibrate the amplifier as instructed in the SoundCheck manual.
2. Calibrate the reference microphone or ear simulator as instructed in the SoundCheck manual.
3. Connect the channel 1 (or Left) output of your soundcard to the input of the amplifier.
4. Connect the output of the amplifier to your device under test. 
5. Position your reference microphone at the desired test distance from the DUT or position the DUT on an ear simulator, and connect the measurement microphone to the microphone power supply.
6. Connect the output of the mic supply to the channel 1 (or Left) input of your soundcard.

You are ready to start the sequence.

 

Further sequence development

Ways in which you could modify or further develop the sequence include:

• Tailor the sequence to a Bluetooth headset or a VoIP phone.  This would include changing the hardware and calibration setups.
• If needed, a period of conditioning signal could be added before the test portion of the speech file plays in order to force the DUT into a stable state.

 

Download Sequence Documentation (PDF)

Download Sequence (Zip file)

To run the sequence in SoundCheck, please save the zip file to your hard drive, then follow the instructions in "Sequence Editor: Exporting/Importing a Sequence' section of the manual. Download Manual.