Triggered Record Using WAV File and 6 Mic Array Test Sequence
A test sequence ideal for measuring in-car audio systems
This sequence allows you to measure a playback system without analog inputs using a 6 microphone array. Specifically, the sequence is designed to measure an in-car audio system. A stimulus WAV file is created in SoundCheck and transferred to the device under test (DUT) where it is played back and the response captured by SoundCheck using a triggered record function. The 6 recordings are batch analyzed to produce individual fundamental curves and the curves are post-processed to produce a single average curve from which an average sensitivity value is calculated.
The default stimulus WAV file may be customized in the stimulus editor. The default stimulus is a stepped sine sweep from 20 kHz to 20 Hz with R10 (1/3 octave) resolution. The stimulus can be saved as a WAV file from the memory list and also during the sequence run, if desired. This file will have the same sample rate and bit depth as the audio interface (in this case, 44.1kHz, 24 bit). By default, the WAV file is automatically normalized to 0 dB FS in the autosave step, so the stimulus level is not important. Note that:
- The parameters of the sweep in the stimulus step are used when creating the WAV file.
- The duration of this stimulus must be considered in the “Time” field of the acquisition step.
- The stimulus step must remain in the sequence and the stimulus settings cannot be changed without re-generating the WAV file with the updated parameters.
- The default stimulus WAV file used in this example is included in the sequence folder.
- Changing the sample rate or bit depth of your audio interface also requires re-saving the WAV file.
- Playback system for WAV stimulus (in this case an in-vehicle audio system)
- SCM-3 calibrated measurement microphone, part # 4004, quantity 6. See recommendations in directions tab for mic array configuration
- Listen SoundConnect 2, 2 channel microphone power supply or equivalent, part # 4026, quantity=3
- Multi-channel audio interface (minimum 6 inputs) such as an RME Fireface UC or equivalent
- SoundCheck Plus (part # 1102) version 16.0 or later
- Eight Channel Acquisition part# 2024
- Equation Editor part # 2012
Triggered Record Acquisition Step Settings
- Mode: Record
- Record type: Triggered
- Time (sec): Must be set to slightly longer than the length of original stimulus sweep plus the Trig. Offset.
- Input Paths: Mics 1 through 6
- Trigger Level: Set level according to background noise and playback level from DUT. Default=70 dBSPL
- Trigger Unit: Set to dB or Pa according to your preference
- Trigger Signal Path: Default= Mic 1
- Trigger Offset (sec): Sets the amount of time that the Acquired Signal is shifted, relative to the point at which it is triggered. Default=-100 ms
- Slope: For triggering on WAV files this should be set to positive. Default=+
- Time Out (sec): Amount of time acquisition will wait for trigger before stopping. Default=10s
Initial Software Setup
When you first open this sequence, you will likely encounter a relink dialog (Figure 3). The purpose of this dialog is to let you know that the Signal Paths used in the sequence (e.g. Mic 1-6) are not present in your Calibration and you will be presented with two options.
- Add the Signal Path to your calibration
- Use an existing signal path, selected from a dropdown menu.
Unless your SoundCheck system is already configured for a 6 mic array, it is recommended that you add the Signal Paths to your calibration. Once you’ve configured the relink dialog, click OK to continue and when prompted, add the calibrated device files to your system. Finally, your Calibration Table View will open and you must assign Hardware Input Channels to the newly added Mic 1-6 Signal Paths.Figure 4: Example Mic Array
A set of six omnidirectional microphones is recommended, with a spacing of approximately 15cm between each microphone. This microphone array should be placed at the approximate intended location of the listeners head, at a slight angle, approximately 30°.
Hardware Setup & Calibration
- Connect the outputs of the mic power supplies to the inputs of the audio interface.
- Connect the microphones to the power supplies and apply the appropriate bias type.
- Calibrate the SCM 3 Reference Microphones as instructed in the SoundCheck manual.
- Position the microphone array at the desired location in the vehicle.
- Transfer the default stimulus WAV file to the system under test
- Alternately, modify the stimulus and save it as a WAV file prior to transfer
- Confirm the WAV file plays from the playback system.
- Set the playback to the desired output level.
- Start the SoundCheck sequence