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.
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 with the Noise Samples per Test option, and the test locations (rows and columns).
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.
Tap the Sine icon to turn on the pink noise generator. This also activates the RTA bars, if enabled, so that you can set an appropriate level.
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.
Tap the + or - button to advance the
test or go back to the previous test location. Tap the icon with the 3
parallel bars to bring up the Test Locations 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 currently selected test is shown with a yellow box
around the dot.
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 - Noise Samples per Test
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.