Room Impulse Response Measurement

SignalScope can acquire room impulse response data by direct capture ("Oscope") or using dual-channel analysis techniques ("Dual FFT").

In its Dual FFT Analyzer tool, SignalScope can measure the room impulse response using dual-channel FFT-based techniques. This approach enables RoomScope to acquire measurement data with high signal- to-noise ratios (SNR), even with little or no averaging (depending on the excitation signal used).

  • The Dual FFT tool can display the impulse response, squared impulse response, or frequency response magnitude of the room. The coherence may also be displayed, which provides an indication of the quality of the measurement, as a function of frequency. A coherence of 1.0 indicates that the measurement was uncontaminated by noise, nonlinearities, or time variance of the system under test (in this context, a room and the loudspeaker(s) and microphone used in the measurement).
  • The Dual FFT Analyzer options menu contains controls for its built-in signal generator, which can produce special excitation signals to excite the room or device under test (DUT).

The Ocope and Dual FFT tools include manual and automatic plot scaling, as well as a data cursor for obtaining precise signal information. Additionally, the current data in each tool can be saved to CSV, TXT, or MAT files. The analyzer display can also be saved to a high resolution PDF file.

Audio Input Path

The audio input path is automatically determined by iOS, according to the external audio hardware, if any, connected to your device (see audio routes).

On current iOS devices the audio input data is generally sampled at 48 kHz. Some audio input accessories may operate at lower sample rates, such as 44.1 kHz, or higher rates up to 192 kHz.

The three typical audio input paths are discussed in greater detail on the following pages:

Dual FFT

For more information, see the Dual FFT Analyzer's main and options pages.


Sometimes, it is more convenient to capture a room impulse response directly by using an impulsive noise to excite the room, such as a starter pistol, hand clap, or balloon pop. In the Oscope tool, different triggering options exist to facilitate the automatic capture of the impulse stimulus and the sound decay that follows.

A place to start may be to set Oscope's time scale to 20 ms/div to capture 2 seconds of data and to set Normal mode triggering with a threshold of 0.25 Pa.

For more information, see the Oscope's main and options pages.