How to Analyze Audio Files with SignalScope


This video shows how to use the MultiTool in SignalScope X to analyze data in an audio file (WAV, AIF, or CAF) using SignalScope’s File Player and Octave Analyzer tools. As an example, a file containing gunshot recordings is analyzed as part of a project to measure the directional nature of gunshot sounds. (Some features shown in this video require the Pro Tool Set.)

SignalScope apps mentioned (SignalScope X version 12.4 was used in this video):


********** Intro (00m 07s)

This video will demonstrate how to analyze data stored in audio files using the Audio File Player and the MultiTool.

Although the file player tool is available in the advanced tool set and can be used for analysis with the other tools in that set, we’ll show, here, that the best way to analyze audio files is with the MultiTool, which requires the Pro Tool Set.

You can follow along with this video in SignalScope X or SignalScope XM, with the Pro Tool Set, or with SignalScope Pro 2022.

The instructions, here, will work whether you’re running SignalScope on your Mac, iPad or iPhone.

Note that tool selection is on the left-hand side of the window, instead of the bottom, if you’re on a Mac.

********** MultiTool Configuration (00m 49.3s)

To get started, let’s select the MultiTool and create a new measurement configuration.

We do that by opening up the tools options menu, entering a name for the new configuration, and then pressing the return key, or the Done button on the virtual keyboard.

This will create a new configuration with the new name.

Now, let’s close the options menu and set up our measurement configuration.

Since the new configuration is just a copy of the previous one, we’ll first remove whatever tools are there to make room for the new ones that we want.

Now in this video, we’ll be analyzing some gunshot recordings that are part of a project to measure the directivity of gunshot sounds.

We want to break the sounds down into individual third-octave frequency bands, so we’ll add an Octave Analyzer tool.

Since the point, here, is to analyze the data contained in audio files, we’ll need to add the File Player tool.

********** Player Configuration (01m 45.5s)

Next, let’s configure the Player tool by loading an audio file.

To do that, click on the import button.

Now we see a list of locations we can add a file from.

Local Configuration Folder refers to a measurement configuration folder belonging to the MultiTool.

Local Folder refers to any folder belonging to SignalScope’s own documents directory.

Music Library refers to available audio files contained within your music library.

External Source refers to files stored elsewhere on your device or system.

In this case, we want to load a file stored on iCloud Drive, so we’ll click the External Source and then browse to the desired file.

So I’ve already got gunshots here in my favorites, so I’m gonna go ahead and load up the gunshot recordings at the zero degree angle.

Once the file loads, you may see this message asking if you would like to automatically calibrate the selected output channels.

This happens when SignalScope detects custom metadata embedded in the audio file containing channel calibration information.

This custom metadata is embedded by the recorder tool in SignalScope or SoundMeter.

In this case, the microphone units and sensitivity were saved by SignalScope when the gunshots were captured using a special measurement microphone.

Since we want to perform calibrated measurements of the gunshot sound levels, let’s choose ‘YES.’

Next, we need to configure our output channel selections.

In the channel selection menu, we can see a list of output channels under each channel of data stored in the loaded audio file.

The player tool lets us choose one or more of these physical or virtual output channels as a destination for the playback of the data in the file.

Since we don’t want to play the gunshot through a speaker, let’s select a virtual output channel.

The V at the end of the channel name indicates that it’s a virtual channel.

We don’t need to route channel 2 anywhere since the gunshot data was only recorded in the first channel of the file.

Now, if we look in the I/O configuration menu, we can select output channels and see that the acoustic units and sensitivity information have been applied to our selected output channel.

One more important point about configuring the file player tool is that we want the hardware sample rate to match the sample rate of the data in the file.

If the sample rates don’t match, sample rate conversion will be used for playback. 

Since we’re making precision measurements, we want to avoid sample rate conversion.

So in order to confirm the sample rate used by the audio file, click on the file info button in the Player tool.

In this case, the gunshot data was sampled at 192 kilohertz.

For convenience, we’ve already connected the RME ADI-2 Pro audio interface that was used for the original recordings.

So we know it supports this sample rate.

Let’s go back to the I/O configuration menu to check the sample rate.

Okay, the device is currently configured for 48 kHz.

So let’s change the desired sample rate to 192k and then confirm that the actual sample rate has in fact changed.

And, there it is.

********** Octave Analyzer Configuration (04m 47.8s)

Now let’s configure the Octave Analyzer tool for the measurements we want.

First, let’s open up this tool’s channel selection menu and make sure we have the same output channel selected that we chose in the Player tool.

In this case, virtual output channel three.

But in this case, let’s turn off auto scale and manually set the scale to 12 dB per division, with a maximum value of 168 dB.

Let’s also show a secondary level and set it to show peak levels.

Next, we’ll set the sound level type to Leq with an indefinite averaging time.

Then, we’ll enable auto stop and set the duration to the smallest available value of 100 milliseconds, since all we want to capture is a gunshot.

We’ll also configure auto start triggering by switching it on, selecting our chosen output channel as the source, and then setting the threshold to an appropriate value.

In this case, let’s set the threshold to 100 pascals, so the measurement will only start when the sound level exceeds 134 decibels.

Finally, we’ll choose a pre-trigger delay of 20 milliseconds to be sure we don’t miss anything just before the level exceeds our threshold.

********** Running the Measurement (06m 30s)

Okay, now we’re ready to start our measurements.

Click the start button at the top of the screen to begin playback and analysis of the data in the file.

Okay, we’ve captured our first gunshot, so I’m gonna pause it.

********** Saving the Measurement (06m 48s)

Now, once the measurement is captured, we could save the measurement to a data file.

To do that, click the action or share button in the top toolbar and select the desired option.

In this case, we’ll click “Save All Data.”

Now, we can edit the name and the type of the data file.

We can also choose to have the data, saved in the file, loaded right back into the analyzer by switching on the switch labeled “Keep Data In Plot.”

Also, since we’re using the Pro Tool Set, we can add custom metadata to the file.

So, let’s go ahead and do that.

Now, we’ll save it.

********** Final Notes (08m 04.2s)

Okay, let’s do one more.

Now, notice that when saving multiple files with the same name, SignalScope will automatically start numbering them.

Another thing to note here is that you can select just a portion of an audio file to analyze, and you can enable repeating playback for cases

in which you would like to let the analysis run for a longer period of time.

To end, here is the Polar Plot showing the directional nature of the gunshots at different frequencies.

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