Using Gated Noise RT60

Gated Noise RT60, also called the Interrupted Noise or Dropped Noise method, is a tool for measuring the reverb decay time in a room. It is based on the international standard ISO 3382, “Acoustics — Measurement of reverberation time of rooms with reference to other acoustical parameters”.

Our implementation uses the interrupted noise method, covering the octave bands from 63 to 4000Hz. Both the T30 and T20 standards are supported. The noise signal is pink noise generated internally using the built-in signal generator in the app.

Available in AudioTools on the App Store

Gated Noise RT60 works well with the internal iOS device microphone, but to meet the standard a Type 1 microphone system is required, such as our iPrecisionMic.

The standard suggests doing several tests at different locations in the room, and for each location, averaging several runs of the test. Gated Noise RT60 supports both of these requirements.

The industry standard metric for room reverb is RT60, which means the amount of time that a sound takes to decay by 60dB. Since it is challenging in the real world to create a test signal that is 60dB above the room abient noise level, the T30 and T20 calculations are used, where a noise signal that decays 30dB or 20dB is used to compute the 60dB decay time.

The standard requires that the test signal noise to be 45dB above the ambient noise floor in the room for T30, and 35dB above the noise floor in the room for T20, for each octave band. Use the markers and the cursor on the RTA bars to check this when you are running tests.

You can turn on RTA bars by tapping the icon on the main screen with the 3 vertical bars. As the tests run, the RTA bars for each octave band are shown in real time. RT60 results appear next to those bands as they are computed.

Settings

Gated Noise RT60 can be customized in several ways. You can set it up to just take single tests, to run and average several tests at one location, or to store and average test data for multiple locations in the room.

Maximum Decay Time

There is a setting to select the maximum decay for the room. Set this to a value larger than what you expect for the room, to allow enough decay time for the signal. The system automatically adjusts the timing of the signal and the pauses between signals to allow a complete test.

T30 and T20

The interrupted noise method works by first turning on the pink noise generator to “charge” room, allowing the test signal to build up to a steady state level, and then measuring that level in each octave band. The noise signal is then turned off, and the system monitors the level, recording the time that the signal is 5dB below the steady state level, and then checking for the signal to reach either 35dB below steady statefor T30, or 25dB below steady state for T20.

This time is then multiplied by the appropriate factor to extrapolate to the RT60 value.

Averages

The standard suggests doing at least 3 tests at each test location in the room, and the system supports that with a selection on the Settings page for the number of Noise Samples Per Test. When the test is started, it will automatically run the number of times specified, and average those results.

Gated Noise RT60 also allows you to set the number of locations in the room that you wish to test. These are organized in rows and columns. For example, you could specify 2 rows of 3 measurements each. As you run tests, the results are stored in the locations, and the final result averages together all of the locations for a single set of results.

Auto-advance Test

To make it easier to run a set of tests at multiple locations in the room, turn on Auto-advance Test. If this is turned on, after a set of T30 or T20 tests are run at one location, the system will automatically advance to the next location, so that you just need to tap the Play/Pause button to start the next location test.

Managing and Viewing Location Tests

Tap the icon on the main screen with 3 horizontal bars. This brings up the Tests page, where you can see all of the tests in a grid. Completeed tests show as green dots, tests not yet completed show as red dots, and the current selected test is shown with a yellow box around the dot.

You can change the selected test to view its results on the main display, or to redo that test. You can also clear the results for a specific location test, or all tests.

Saving and Recalling Files

To save the results of a Gated Noise RT60 file, tap the folder icon on the lower left side of the toolbar on the bottom of the screen. This will being up the Save / Recall page.

Save the file by entering a file name and tapping Store File on the the popup that appears.

To recall a stored file, select it from the list to highlight it, and then tap Recall to bring up the results. Note that recalling a stored file replaces the information on the main page.