speechIntelligibilityIndex
R2026bMeasure speech audibility using speech intelligibility index (SII) metric
Since R2026b
Syntax
Description
specifies options using one or more name-value arguments, such as the filter bank
method. Some name-value arguments are required for specific SII calculations. For more
information, see Speech Intelligibility Index Input Arguments.[___] = speechIntelligibilityIndex(___,Name=Value)
speechIntelligibilityIndex(___) without any output
arguments plots a bar chart of equivalent speech and noise levels per band, overlaid
with the BAF.
Examples
Create a vector of distances from 0.5–20 m at increments of 0.5 m.
d = 0.5:0.5:20;
Calculate the SII for each vocal effort and each distance. Use the default speech and noise profiles for 1/3 octave bands.
sii = nan(4,numel(d)); for ii = 1:numel(d) sii(1,ii) = speechIntelligibilityIndex( ... Method="1/3 octave band", ... VocalEffort="normal", ... Distance=d(ii)); sii(2,ii) = speechIntelligibilityIndex( ... Method="1/3 octave band", ... VocalEffort="raised", ... Distance=d(ii)); sii(3,ii) = speechIntelligibilityIndex( ... Method="1/3 octave band", ... VocalEffort="loud", ... Distance=d(ii)); sii(4,ii) = speechIntelligibilityIndex( ... Method="1/3 octave band", ... VocalEffort="shout", ... Distance=d(ii)); end
Plot the SII for each vocal effort as a function of distance between speaker and listener.
plot(d,sii) grid on title("Speech Intelligibility Index (SII)","Quiet Free-field, 1/3 octave band") xlabel('Distance (m)') ylabel('SII') legend('Normal','Raised','Loud','Shout',Location="SouthWest")
Investigate the effect of ear devices on the speech intelligibility index.
Define octave-band center frequencies and typical attenuation in dB SPL for foam earplugs.
freq = [250,500,1000,2000,4000,8000]; attenuation = [41,45,44,36,43,47];
Compare the SII for shouting speech levels in a loud environment with and without hearing protection.
noiseSpectrum = [73 70 64 59 54 50]; figure tiledlayout(2,1,TileSpacing="compact") nexttile speechIntelligibilityIndex(NoiseLevel=noiseSpectrum,... VocalEffort="shout") subtitle("Without Hearing Protection") nexttile speechIntelligibilityIndex(NoiseLevel=noiseSpectrum,... VocalEffort="shout",... InsertionGain=-attenuation) subtitle("With Hearing Protection")
Define the typical hearing loss in dB HL for adults aged 60–69 and octave band gain in dB SPL for hearing aids.
hearingLoss = [25,25,25,40,40,40]; aidGain = [10,10,20,30,30,40];
Compare the SII for normal speech and noise levels without and with hearing aids.
figure tiledlayout(2,1,TileSpacing="compact") nexttile speechIntelligibilityIndex(HearingThreshold = hearingLoss) subtitle("Without Hearing Aids") nexttile speechIntelligibilityIndex(HearingThreshold = hearingLoss,... InsertionGain=aidGain) subtitle("With Hearing Aids")
Calculate the SII from room impulse response simulations using the methods in clause 5.2 of the ANSI/ASA S3.5-1997 standard.
Read a recording of a washing machine to simulate background noise in a space. Calculate the length of the recording in seconds.
[noise,fs] = audioread("Engine-16-44p1-stereo-20sec.wav"); noise = mean(noise,2); % convert to mono duration = numel(noise)/fs; % seconds
Generate two room impulse responses of a shoebox room using acousticRoomResponse. The responses simulate measurements at the center of a listener's head. Generate the first response from the location of a speaker (1 m from the listener) and the second response from the location of the noise source (3 m from the listener).
room = [4, 6, 6]; % meters
headLoc = [2, 2.5, 1.75];
speakerLoc = [2, 3.5, 1.75];
noiseLoc = [2, 5.5, 1.75];
irSpeaker = acousticRoomResponse(room,speakerLoc,headLoc,SampleRate=fs);
irNoise = acousticRoomResponse(room,noiseLoc,headLoc,SampleRate=fs);Convolve the noise signal with the impulse response generated from the noise source location. Measure the equivalent continuous sound level (Leq) of the noise in the room using splMeter. This example treats the noise signal as if it was recorded using a calibrated microphone. For real measurements, use a signal recorded with a calibrated microphone or provide a calibration factor when creating the splMeter object.
noiseInRoom = fftfilt(irNoise,noise); meter = splMeter(SampleRate=fs,... FrequencyWeighting="Z-weighting",... Bandwidth="1 octave",... FrequencyRange=[250,8000],... TimeInterval=duration); [~,noiseLeq] = meter(noiseInRoom); noiseLeq = noiseLeq(end,:); % use final reading
Generate a speech spectrum excitation signal with the same duration as the audio recording using siiExcitation. To simulate a calibrated real-world excitation, set Normalize to false.
[~,speechExcitation] = siiExcitation(fs, ... Method="octave band", ... Duration=duration, ... VocalEffort="shout", ... Normalize=false, ... OutputMode="merged");
Convolve the speech excitation with the impulse response generated from the speaker location. Combine the noise and filtered speech signal and measure the combined speech and noise level (CSNSL).
speechInRoom = fftfilt(irSpeaker,speechExcitation);
speechAndNoise = speechInRoom+noiseInRoom;
release(meter);
[~,csnsl] = meter(speechAndNoise);
csnsl = csnsl(end,:); % use final readingCalculate the speech intelligibility index using the simulated impulse response from the speaker location, CSNSL, and noise levels.
speechIntelligibilityIndex(irSpeaker,fs, ... SpeechAndNoiseLevel=csnsl, ... NoiseLevel=noiseLeq)
Calculate the SII from recordings made at the eardrum using the methods in clause 5.3 of the ANSI/ASA S3.5-1997 standard.
Use sofaread to load a Spatially Oriented Format for Acoustics (SOFA) file with generic head-related impulse responses (HRIRs). Choose the index that corresponds to a source directly in front of the listener.
s = sofaread("ReferenceHRTF.sofa"); mIndex = 7; fprintf("Azimuth: %0.f. Elevation: %0.f. Radius: %0.f.\n",s.SourcePosition(mIndex,:));
Azimuth: 0. Elevation: 0. Radius: 4.
Get the HRIR at the selected position for the left ear and the sample rate of the HRIR.
fs = s.SamplingRate; hrir = squeeze(s.Numerator(mIndex,1,:));
Generate the SII excitation signals with siiExcitation. To simulate a calibrated real-world excitation, set Normalize to false.
duration = 16; [mtfExcitation,speechExcitation,levels] = siiExcitation(fs, ... Method="octave band", ... Duration=duration, ... Normalize=false, ... OutputMode="merged");
Use pink noise to simulate a noise source. Convolve the speech excitation and noise signal with the HRIR. Combine the noise and filtered speech signal and measure the combined speech and noise level (CSNSL).
noise = 0.25*pinknoise(duration*fs); speechAndNoise = fftfilt(hrir,speechExcitation+noise);
Use splMeter to measure the CSNSL.
meter = splMeter(SampleRate=fs,... FrequencyWeighting="Z-weighting",... Bandwidth="1 octave",... FrequencyRange=[250,8000],... TimeInterval=duration); [~,csnsl] = meter(speechAndNoise); csnsl = csnsl(end,:); % use final reading
Convolve the MTF excitation and noise signals with the HRIR to generate the system response.
mtfResponse = fftfilt(hrir,mtfExcitation+noise);
Use the excitation and response signals to calculate the SII. Set SpeechMeasurementLocation and NoiseMeasurementLocation to "eardrum" to indicate that measurements were taken in-ear.
speechIntelligibilityIndex(mtfResponse,mtfExcitation,fs, ... SpeechAndNoiseLevel=csnsl, ... Method="octave band",... SpeechMeasurementLocation="eardrum", ... NoiseMeasurementLocation="eardrum")
Input Arguments
Name-Value Arguments
Output Arguments
More About
References
[1] American National Standards Institute (ANSI). 1997. "Methods for calculation of the speech intelligibility index." ANSI/ASA S3.5-1997 (R2024). ANSI, approved June 6, 1997; reaffirmed September 5, 2024.
[2] IEC 60268-16:2020. "Sound system equipment — Part 16: Objective rating of speech intelligibility by speech transmission index." International Electrotechnical Commission.
Extended Capabilities
Version History
Introduced in R2026b
