STIPA Operation Guide
This is the help guide for STIPA, the speech intelligibility measurement tool. STIPA works by analyzing how much of the amplitude oscillations embedded in a special audio test signal can be extracted, to determine how easy it will be to understand someone speaking in the room, and by extension how well a sound system will be understood.
STIPA has been adopted by many local and national fire codes and other public standards as the tool of choice for measuring speech intelligibility.
Our implementation of STIPA is based on v4 of the standard and complies with all sections of the standard.
STIPA Pro and STIPA Basic
This guide applies to both STIPA Pro and STIPA Basic. The same calculation algorithms are used for both modules. STIPA Pro includes the option to turn on an off level-dependent auditory masking, STIPA Basic does not.
STIPA Basic does not include Save / Recall, Save to Photo Roll, Test Averaging, LEQ Display, and the Detail View screen. It is suitable for field STIPA measurements, and uses the same test signals as STIPA Pro
STIPA Compliance Study
This section describes how to use STIPA to measure speech intelligibility.
The STIPA signal will be played in the room, and STIPA module will sample the signal using the built-in iOS device microphone, or an external mic. Results will be shown as the test is running, and at the end of the test.
You can play the STIPA signal from the App itself, or you can download it from our website and burn it to a CD. Do not alter the signal in any way and avoid compressing it (keep it as a WAV file, do not change to AAC or MP3 in iTunes). Also, if the sample rate of the playback device varies from the sample rate that the iOS device is running at by more than a few percent, it will skew the results.
Running a STIPA Test
Once you have the signal playback set up, you are ready to run a test. Note which of the 6 test result slots is selected (the highlighted segment), as this is the test number that the results will be stored in. (See Averaging, below).
Start the signal playing, and tap the RUN button. The test signal analysis will begin, and you will see a progress bar begin to move across the screen. While the test is running, the only other sound should be normal room background noise. At the end of the test (20 seconds), the test will automatically stop. You can stop the test before 20 seconds have completed, and the results of the tests up to that point will be shown, but they may not be as precise or accurate as a full 20 second test.
At the end of the test you can see the STIPA overall value (the large number on the screen), or you can inspect the individual m1 and m2 values by tapping the Details button.
While the test is running, the SPL levels for each of the octave bands, and the overall SPL level, are shown on the screen. At the completion of the test, the Leq (average SPL) for the entire test are shown, and stored with the test results, so that they can be recalled at a later time.
Averaging – Pro Feature
The STIPA standard suggests averaging six 15-second tests, and discarding or repeating any tests that vary more than 0.02 from the mean. To provide for this, we have set up our App with 6 test slots, and an average button. Select any of the 6 test slots and run a test. When complete, the test slot number will be green. This only indicates that a test has been completed for this test slot number, not the test pass/fail status. Unused test slots will appear in red. The number of completed tests will be shown below the test slot selector.
You can select test slots at any time by tapping the number of the test. To view the average of all of the completed tests, tap the ҁvgӦ#10;button.
Adding Occupational Noise to a Test Run – Pro Feature
There may be situations where you wish to run a test during time that is not representative of the normal use of the space. For example, it may be more convenient to run the test at night, when the space is not occupied, but then you would be missing the inclusion of the normal occupational noise of the space during the day. Note that this feature requires running STIPA as a part of the AudioTools app. Contact support of you do not have this, or just download AudioTools from the app store.
In this case you can save recording of the noise during the day and add it to the test that you are running at night. To do this, follow these steps:
– Record the Noise Navigate to the Recorder module, on the Utilities menu. Go to the settings page, and select Mono, 48kHz sample rate, and WAV compression (none). Turn off Record Monitor to prevent feedback. On the recording page, make sure the gain slider is set to 0dB. Now record a sample of the occupational noise in the space. You should make this recording longer than a typical STIPA test, but if it is shorter the recording will be looped during the test run. Save this recording using the Save/Recall page, and make note of the name.
– Select the Recorded Noise When you are ready to do the test, from the STIPA module, select the settings page, and tap the button under the Added Occupancy Noise label. This may say “Select Stored Audio File”, or it may be the name of a previously selected file. Pick the desired noise file from the list and tap recall. If the file sample rate is not correct you will see an error message. Tap Done to return to the main screen.
– Run the Test Run the test as usual. The recorded noise file will be silently mixed in with the live incoming audio prior to the STIPA calculations. You will see “Using External Noise File” on the screen beneath the test selector.
– Clearing the Noise File If you no longer wish to use the recorded noise, you can either go to the settings page and tap “Clear Noise File” or simply exit back to the menus and re-open STIPA.
There are several items shown on the screen for each test.
Overall STIPA value This value is shown in large digits on the screen. Larger numbers are better, i.e. 1.00 is “perfect”.
Tests Status Completed tests are shown in green on the test selector bar, and unused test slots are shown in red. Tap Avg to see the average of all completed tests.
Test Qualification Band One of the letter slots will be highlighted, indicating the relative speech intelligibility level. The highlight is also color-coded,with green = good or excellent, yellow = fair, and red = poor.
SPL Leq This graph shows the Leq (average SPL) of each octave band of the test.Use it as a guide to see the signal SPL level for each octave band of the test. The yellow band on the right indicates the current SPL level at all times andis not related to the completed test results.
– Pro Feature
Sample Rate Variations
If you play the test signal from your iOS device, the sample rate of the signal will match what the STIPA module is expecting. However, if you play the test signal from an external source, it is possible that the sample rate of that external device will not be exactly 44100Hz, and you may not get reliable STIPA results. To test the sample rate of the external player, find or create a sine wave signal that is at a known frequency, preferably above 4000 Hz. Play that signal while you are running the FFT module in AudioTools, and turn on Peak Tracking. Set the FFT Size to 16384 or greater.
Note the frequency display for the test signal. It needs to be within 0.05%, or 2 Hz in 4000 Hz., or 4 Hz in 8000 Hz.
Save / Recall – Pro Feature
When you save a STIPA test, all completed tests (up to 6) will be stored under the test name, and will be recalled anytime that you recall the test. Also, results from all completed tests will be included in the tab-delimited XLS file that is created when you save results. Use the normal Export function on the Save / Recall screen to export this data to a computer.