Sound Spectrum Pro for Windows

Impulse response and RT60

Shows the way the sound pressure level would evolve in the case of a very loud and short sound (like a gun shot).
Choose it from the Mode menu.
The impulse response is calculated from the room's response to a pink sweep signal (slightly nicer than firing a gun).
The graph is scaled with reference to the max direct sound.
The volume is controlled by the slider on the top, and also by the general music volume controls of the device.
Choose a frequency band from the Trace menu, from:
- 20Hz - 12kHz - Full bandwidth.
- Octave band - with centers from 31.5Hz to 8kHz. Up/down keys cycle through these bands.
- 1/3 Octave band - sub-bands of the current 1-octave band. Left/right keys cycle through these sub-bands.
We recommend using an amplifier, real speakers, and maybe a good external mic. For most devices, the built-in speakers and mic may not give very good results, especially at low frequencies. The sound should be loud enough, but avoiding any distortion.
The loopback signal has a virtual echo at 1 second.

FFT size - Larger values will give longer analysis time (up to 20 seconds for 1M). Less than 64k will not work very well.
Window type - Rectangular is the "correct" setting, but you can experiment with others. Please note that the rectangular window will give weird-looking shapes with loopback modes - this is because the sweep signal is shorter than the measurement interval.
Smoothing time constant - Not used.
Calibration - Not used.