Open loop testing allows devices with cloud-based, Bluetooth, and other wireless connections to be measured.
In conventional audio tests, for example speaker and microphone measurements, the stimulus playback and response recording occur simultaneously. The two signals are correlated, and ready to analyze. When speakers and microphones are incorporated into devices such as mobile phones and smart speakers, there is no longer a simultaneous input/output audio path, so we need open loop testing to measure the speakers and microphone.
Open loop testing is simple in SoundCheck, since its architecture has always allowed analysis to be performed independently of acquisition. In fact, Listen pioneered open loop testing, originally for testing MP3 players, back in 2006 – long before others started implementing this capability.
In open loop testing, the stimulus includes a trigger to tell SoundCheck when to start recording. SoundCheck features three different trigger options. The simple level trigger starts recording when the signal reaches a pre-defined level. The level and frequency trigger is more robust and features a short fixed-frequency sine tone played at the start. This triggers the recording but is not analyzed. Our newest level and cross correlation trigger uses a chirp-based conditioning tone and is much less susceptible to false triggers, especially in noisy environments or where there are other test stations playing similar test tones nearby.
Once the recording is captured, advanced algorithms resample and frequency shift the response to align it with the stimulus prior to analysis. SoundCheck also includes proprietary algorithms to compensate for delay between stimulus and response, including the latest Autodelay+ algorithm which accounts for the longer latencies seen when sending test signals via the cloud.
Open Loop Testing Demonstration
In this short video, we make audio measurements on a pair of Bluetooth connected smart glasses using an open loop test.
This video demonstrates the various trigger options available in open loop testing
Learn more about SoundCheck’s measurement modes:
Virtual Instruments | Test Sequences | Offline Analysis | Open Loop Testing
