stoi

Short-time objective intelligibility measure

Since R2024a

Syntax

metric = stoi(processed,reference,fs)

Description

metric = stoi(processed,reference,fs) returns the short-time objective intelligibility (STOI) measurement. STOI is a speech intelligibility metric that compares the processed speech signal with a clean reference signal.

Examples

Use STOI to Measure Intelligibility of Noisy Speech

Read in an audio file containing a clean speech signal. Add pink noise to create a noisy speech signal.

[cleanSpeech,fs] = audioread("Rainbow-16-8-mono-114secs.wav");
noisySpeech = cleanSpeech + 0.1*pinknoise(size(cleanSpeech));

Use stoi to measure the intelligibility of the noisy speech signal with the clean speech as the reference signal.

metric = stoi(noisySpeech,cleanSpeech,fs)

metric = 0.9811

Recreate the noisy speech signal with more pink noise and measure the intelligibility. See how the noisier signal has lower intelligibility according to the STOI metric.

noisySpeech = cleanSpeech + 3*pinknoise(size(cleanSpeech));
metric = stoi(noisySpeech,cleanSpeech,fs)

metric = 0.5943

Use STOI to Evaluate Enhanced Speech Signal

Read in an audio file containing speech and noise. Also read in an audio file containing the original clean speech to use as a reference signal.

[noisySpeech,fs] = audioread("NoisySpeech-16-mono-3secs.ogg");
reference = audioread("CleanSpeech-16-mono-3secs.ogg");

Calculate the STOI metric for the noisy speech signal using stoi.

noisySpeechSTOI = stoi(noisySpeech,reference,fs)

noisySpeechSTOI = 0.8370

Use enhanceSpeech to enhance the speech signal. Evaluate the enhanced signal using the STOI metric and see the improvement compared to the STOI of the noisy signal.

enhancedSpeech = enhanceSpeech(noisySpeech,fs);
enhancedSpeechSTOI = stoi(enhancedSpeech,reference,fs)

enhancedSpeechSTOI = single
    0.8808

Input Arguments

processed — Processed speech signal

column vector

Processed speech signal, specified as a column vector (single channel) with the same size as reference. STOI measures the intelligibility of this processed signal.

Data Types: single | double

reference — Reference speech signal

column vector

Reference speech signal, specified as a column vector (single channel) with the same size as processed. The STOI metric compares the processed signal with this reference signal to measure the intelligibility.

Data Types: single | double

fs — Sample rate (Hz)

positive scalar

Sample rate of both the processed and reference signals in Hz, specified as a positive scalar.

Data Types: single | double

Output Arguments

metric — STOI metric

scalar in range [-1,1]

STOI metric, returned as a scalar in the range [-1,1]. STOI measures the intelligibility of the processed input signal by comparing it with the clean reference signal. A higher value for the metric corresponds to a more intelligible speech signal.

References

[1] C. H. Taal, R. C. Hendriks, R. Heusdens and J. Jensen, "A short-time objective intelligibility measure for time-frequency weighted noisy speech," 2010 IEEE International Conference on Acoustics, Speech and Signal Processing, Dallas, TX, USA, 2010, pp. 4214-4217, doi: 10.1109/ICASSP.2010.5495701.

[2] C. H. Taal, R. C. Hendriks, R. Heusdens and J. Jensen, "An Algorithm for Intelligibility Prediction of Time–Frequency Weighted Noisy Speech," in IEEE Transactions on Audio, Speech, and Language Processing, vol. 19, no. 7, pp. 2125-2136, Sept. 2011, doi: 10.1109/TASL.2011.2114881.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Version History

Introduced in R2024a