Impulse Response Measurer Walkthrough

In this tutorial, explore key functionality of theImpulse Response Measurer. TheImpulse Response Measurerapp enables you to

Configure your audio I/O system.
Acquire impulse response (IR) measurements using either the exponential swept sine (ESS) or maximum length sequences (MLS) methods.
View and manage captured IR data.
Export the data to a file, workspace, or other app for further study.

To begin, open theImpulse Response Measurerapp by selecting theicon from the app gallery.

Configure Audio I/O System

TheImpulse Response Measurerapp enables you to specify an audio device, sample rate, samples per frame, player channel, and recorder channel. The audio device must be a real or virtual device enabled for simultaneous playback and recording (full-duplex mode) and must use a supported driver. Supported drivers are platform-specific:

Windows^®–– ASIO™: Click thebutton to open the settings panel for the ASIO driver.
Mac–– CoreAudio
Linux^®–– ALSA

Valid values for sample rate and number of samples per frame depend on your specified audio device.

You can use the level monitor toverify the configuration of your audio I/O system.

Configure IR Acquisition Method

To configure your IR acquisition method, use theMethodandMethod Settingssections of the toolstrip.

You can select the method to acquire IR measurements as either:

Maximum Length Sequences(MLS)
Exponential Swept Sine(Swept Sine)

Both methods for IR acquisition have the same basic settings, including:

Number of Runs–– Number of times the excitation signal is sent within a single capture. Multiple runs are used to average individual impulse response captures to reduce measurement noise.
Duration per Run (s)–– Total time of each run in seconds.
Excitation Level (dBFS)–– The level of the excitation signal in dBFS.

Both methods for IR acquisition also have the same advanced run settings, including:

Wait before first run–– Delay before starting first run. The delay allows time for any last-minute tasks, such as exiting a room before testing its acoustics.
Pause between runs–– Duration of the pause between runs. During a pause, the excitation signal is not sent, and audio is not recorded. When using theSwept Sine冰毒od, include a pause between runs to avoid buildup of reverberations. Pause between runs is always zero for theMLS冰毒od.
Number of warmup runs–– Number of times to output the excitation signal before acquisition. TheMLS冰毒od assumes the signal it acquires is a combination of the excitation signal and its impulse response. Use warmup runs to remove transients.

The total capture time is a sum of run durations, pauses, and the initial wait.

TheSwept Sine冰毒od has additionalAdvanced Settingsto control the excitation signal, including:

Sweep start frequency
扫描频率停止
Sweep duration
End silence duration

When using theSwept Sine冰毒od, theRun Durationis divided intoSweep durationandEnd silence duration. During the end silence, the app continues to record audio, enabling acquisition of the response over the entire range of the frequency sweep.

Starting in R2022a, you can automatically save device, method, and advanced settings and use them in future measurement sessions.

Acquire IR Measurements

For this example, use theMLS冰毒od with default settings. Once you have your audio device set up, clickCapture. A dialog box opens that displays the progress of your capture. IR measurements are captured twice.

Impulse and magnitude responses acquired from audio device.

Analyze and Manage IR Measurements

After the capture, theImpulse Response Measurerapp stores the captured data locally. TheData Browserdisplays the title of the captured data, the colors used for plotting, and information about the settings used to acquire the data. You can double-click a color in theData Browser你想要选择哪种颜色与eac有关h impulse response. You can also double-click the title to rename your captured data. Rename your captures asFirstCaptureandSecondCapture, and change the colors to pink and green. To make one impulse response plot appear on top of the other, select the title in theData Browser. Select the capture you relabeledFirstCapture.

Impulse and magnitude response plots of captured data.

By default, the impulse response and magnitude response are plotted. You can view any combination of the impulse, magnitude, and phase response using theLayoutbutton. Minimize theData Browser, then select thePhase Response.

Impulse Response Measurer app display menu.

Impulse, magnitude, and phase response plots.

You can toggle the relative size of the plot by moving the dividers. You can zoom in and out or toggle between linear and logarithmic frequency axes by selecting the icons that appear when your pointer is over the plot. Updating either the magnitude response or the phase response updates the other. Zoom in on the impulse response plot and in the range 0–20 Hz of your frequency response plots. Zooming in, you can see the small delay betweenFirstCaptureandSecondCapture. When the zoom level is high enough, line markers automatically appear.

Zoomed in impulse, magnitude, and phase response plots.

Export IR Measurements

To view export options for further analysis or use, clickExport.

Export the data to your workspace. The data is saved as a table. To inspect how the data is saved, display the table you exported.

irdata_111104

irdata_111104 = 2×16 table TimeOfCapture ImpulseResponse Device SampleRate SamplesPerFrame PlayerChannels RecorderChannel Method NumRuns DurationPerRun ExcitationLevel RawAudioData SamplesDropped OtherMetaData MagnitudeResponse PhaseResponse __________________________ _______________ ____________________ __________ _______________ ______________ _______________ ______ _______ ______________ _______________ ____________ ______________ _____________ _________________ _____________ FirstCapture 20-Oct-2021 11:01:22 -0400 1×1 struct "Focusrite USB ASIO" 44100 1024 {[1]} 1 "MLS" 2 0.5 -6 1×1 struct 0 1×1 struct 1×1 struct 1×1 struct SecondCapture 20-Oct-2021 11:01:29 -0400 1×1 struct "Focusrite USB ASIO" 44100 1024 {[1]} 1 "MLS" 2 0.5 -6 1×1 struct 0 1×1 struct 1×1 struct 1×1 struct

When you export the data as a MAT-file, the same table is saved as when you export to the workspace. When you select to export the data as a WAV file, each impulse response is saved as a separate WAV file. The title of the capture is the name of the WAV file. In this example, selecting to export data to audio WAV file places two WAV files in the specified folder,FirstCapture.wavandSecondCapture.wav.

To analyze your captured data further, view the data in theFilter Visualization ToolorSignal Analyzer应用程序。