Smaart 7 Impulse Response Measurement and Analysis Guide Copyright 2015 Rational Acoustics, LLC. All rights reserved. Introduction .................................................................................................................................................. 1 Scope and purpose of document .............................................................................................................. 1 1: What is an impulse response? .................................................................................................................. 2 Anatomy of an acoustical impulse response ............................................................................................ 3 Propagation Delay ................................................................................................................................. 3 Arrival of Direct Sound .......................................................................................................................... 4 Discrete Reflections .............................................................................................................................. 4 Early Decay, Reverberant Build-up, and Reverberant Decay ............................................................... 4 Noise Floor ............................................................................................................................................ 4 Uses for impulse response measurement data ........................................................................................ 5 Delay Time Measurement ..................................................................................................................... 5 Reflection Analysis ................................................................................................................................ 5 Reverberation Time (T60, RT60…) ........................................................................................................ 5 Early Decay Time (EDT) ......................................................................................................................... 5 Early-to-late energy ratios .................................................................................................................... 6 Speech Intelligibility Modeling .............................................................................................................. 6 2. A Quick Tour of the Smaart 7 Impulse Response Mode User Interface ................................................... 7 1. Navigation pane ................................................................................................................................ 7 2. Main Graph Area ............................................................................................................................... 8 3. Cursor Readout ................................................................................................................................. 9 4. Sound Level Meter ............................................................................................................................ 9 5. Data Display Controls ........................................................................................................................ 9 6. Signal Generator ............................................................................................................................. 10 7. FFT size and Averaging Controls ..................................................................................................... 10 8. Input Source Selector ...................................................................................................................... 10 9. Live Measurement Controls ............................................................................................................ 10 10. Bandpass Filters ............................................................................................................................ 11 Additional Options for IR Measurement ................................................................................................. 11 General Options Pertaining to IR Measurement ................................................................................ 11 Impulse Response Options .................................................................................................................. 12 3: Analyzing Impulse Response Data .......................................................................................................... 14 i | P a g e Copyright 2015 Rational Acoustics, LLC. All rights reserved. Time Domain Analysis ............................................................................................................................. 14 Logarithmic Time Domain Display ...................................................................................................... 14 Linear Time Domain Display ............................................................................................................... 15 Energy Time Curve (ETC) ..................................................................................................................... 17 Bandpass Filtering ............................................................................................................................... 19 Discrete Reflections ................................................................................................................................ 19 Reverberation Time ................................................................................................................................ 20 Reverse Time Integration .................................................................................................................... 20 Evaluation Ranges (EDT, T20, T30)...................................................................................................... 21 Reporting Results for Reverberation Time ......................................................................................... 23 Early-to-Late Energy Ratios ..................................................................................................................... 24 Clarity Ratios (C35, C50, C80…) ........................................................................................................... 24 The Histogram Display ............................................................................................................................ 25 The All Bands Table ................................................................................................................................. 26 Frequency Domain Analysis .................................................................................................................... 26 The Spectrograph .................................................................................................................................... 27 Spectrograph Time and Frequency Resolution ................................................................................... 29 Spectrograph Dynamic Range ............................................................................................................. 31 Spectrograph Analysis of an Acoustical Impulse Response ................................................................ 31 Speech Intelligibility Metrics ................................................................................................................... 32 STI and STIPA ....................................................................................................................................... 32 ALCons ................................................................................................................................................. 35 4: Measuring an Acoustical Impulse Response ........................................................................................... 36 What are we measuring, and why? ........................................................................................................ 36 Direct vs Indirect IR measurement ......................................................................................................... 36 Direct IR Measurement Using an Impulsive Stimulus ............................................................................. 36 Indirect (Dual Channel) IR Measurement ............................................................................................... 37 Dual Channel IR measurement Using Period-Matched Signals .......................................................... 38 Dual Channel IR measurement Using Random Stimulus Signals ........................................................ 41 Selecting Excitation Sources and Positions ............................................................................................. 42 Minimum Distance from Sound Sources ............................................................................................ 43 ii | P a g e Copyright 2015 Rational Acoustics, LLC. All rights reserved. Directional Loudspeakers and Reverberation Time ............................................................................ 44 Selection of Measurement Positions ...................................................................................................... 45 Selecting Measurement Parameters ...................................................................................................... 46 Input source .......................................................................................................................................