1Acousteen, Herman Steeneken

Past, Present and Future of STI

Herman J. M. Steeneken (www.steeneken.com)

2Acousteen, Herman Steeneken

Past: STI (1971, 1980), Envelope Spectrum (1972), MTF (1975), RASTI (1979), prediction by ray-tracing(1981), IEC 60268-16 (1988, 1998)

Present: Revised STI (1992, 1999, 2002), STIPA (2001), IEC 60268-16 (2003), ISO 9921 (2003)

New and Future: Binaural STI, improvement measurement STI from speech signal, non-native speech, vocoders

3Acousteen, Herman Steeneken

Signal-to-Noise ratio !!!

4Acousteen, Herman Steeneken

Assessment Methods

• Subjective assessment with subjects (speakers

and listeners): representative, limited

reproduction, no diagnostics, laborious

• Objective assessment based on physical

properties (measurements): reproducible,

diagnostic, fast

• Objective methods allow prediction of system

performance: design tool

5Acousteen, Herman Steeneken

Speech and Noise

6Acousteen, Herman Steeneken

Speech envelope function and envelope spectrum

7Acousteen, Herman Steeneken

Spatial line frequency equivalent to MTF

8Acousteen, Herman Steeneken

Distortion of Speech Envelope

9Acousteen, Herman Steeneken

Dynamic measurement of SNR

10Acousteen, Herman Steeneken

Matrix for seven MTF’s

1 Hz

X

3 Hz

10 Hz

11Acousteen, Herman Steeneken

CALCULATION of STI

12Acousteen, Herman Steeneken

Calculation scheme

13Acousteen, Herman Steeneken

Frequency weightings (various studies)

octave-band centre frequency (Hz)

freq

uenc

y-w

eigh

ting

fact

or

0.0

0.1

0.2

0.3

0.4

0.5

125 250 500 1k 2k 4k 8k

nonsense syllables (Pavlovic et al. 1984, ANSI S3.5)PB-words (Steeneken et al. 1980, IEC 60268-16)initial consonants (Steeneken, 1992)vowels, (Steeneken, 1992)

14Acousteen, Herman Steeneken

Redundancy with image detection

15Acousteen, Herman Steeneken

Frequency weightings (CVC words)

octave-band centre frequency (Hz)

fre

qu

en

cy-w

eig

htin

g fa

cto

r

0.0

0.1

0.2

0.3

0.4

0.5

125 250 500 1k 2k 4k 8k

CVC words male speech female speech

MTI + .... + )MTIMTI(

- MTI + )MTIMTI( - MTI = STI

77322

2221111r

16Acousteen, Herman Steeneken

Relation Noise and Band-pass limiting

STI r

CV

C-w

ord

scor

e (%

)

1

2

3

4

5

6

78

9

10

11

12

13

14

15

16

17

18

0

20

40

60

80

100

0.0 0.2 0.4 0.6 0.8 1.0

male speech

S.d.= 4.4%

Male speech

17Acousteen, Herman Steeneken

Listening test with four subjects

18Acousteen, Herman Steeneken

Embedded CVC words:

versta des overen nu fijs uithet woord zek eindenoteer lal punt

“Semi random” combinationof:

17 initial consonants15 vowels11 final consonants

19Acousteen, Herman Steeneken

Relation AGC and echoes

S.d.= 6.9 %

Male speech

STI r

CV

C-w

ord

scor

e (%

)

33

34

35

36

37

38

39

4041

42

43

44

44

45

46

47

48

49

50

51

52

53

54

55

0

20

40

60

80

100

0.0 0.2 0.4 0.6 0.8 1.0

male speech

20Acousteen, Herman Steeneken

Qualification of STI (Acustica, 1984)

21Acousteen, Herman Steeneken

Performance cabin public address

22Acousteen, Herman Steeneken

Iso-STI contours

23Acousteen, Herman Steeneken

Effective gain of a PA-system

24Acousteen, Herman Steeneken

Field measurement

25Acousteen, Herman Steeneken

Full STI (STI-14 and limited modulation frequency range STI-3)

STI-14

• Seven octave bands

• 14 Modulation frequencies

• Random envelope for octaves not under test

STI-3

• Seven octaves

• 3 Modulation frequencies (1.0, 3.15, and 10 Hz)

• Random envelope for octaves not under test

26Acousteen, Herman Steeneken

RASTI (Room Acoustics STI,1979)

Only for person-to-personcommunication assessment

Two octave bands(500Hz and 2 kHz)

Complex envelope(4 and 5 mod. freq.)

see Acustica 1984, IEC 60268-16

27Acousteen, Herman Steeneken

STI-PA (STI Public Address, 2001)

Assessment of Public Address

including: acoustic environment,band-pass limiting, overload dis-tortion

Seven octave bands (125 Hz and 250 Hz merged)

Complex envelope (2 simultaneous modulation frequencies per band)

see IEC 60268-16

28Acousteen, Herman Steeneken

Future

• Binaural STI

• Improvement using Speech as test signal

• Non-native talkers and listeners

29Acousteen, Herman Steeneken

Future: Binaural STI (I)

Use artificial head and perform

simultaneous measurement on both ears

Select highest performance (best ear

selection)

Use cross correlation approach for 500,

1000, and 2000 Hz.

30Acousteen, Herman Steeneken

Future: Binaural STI (II)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

10

20

30

40

50

60

70

80

90

100

22

27

33

39

37

3 7

2523

19

417

28

35

15

13

9

1

31

38

5

18

32

20

26

6

1116

2

29

24 14

10

8

21

12

3634

30

STI

CV

C w

ord

scor

e (%

)

monaural CVC vs STIMean ear STIBinaural STI

31Acousteen, Herman Steeneken

Future: improvement Speech Signal as test signal

32Acousteen, Herman Steeneken

Future: non-native talkers and listeners

L1 L2

-12 -6 0 6 12 0

10

20

30

40

50

60

70

80

90

100

Speech-to-noise ratio (dB)

spee

ch in

telli

gibi

lity

(% c

orre

ct)

resp

onse

s)

0.10 0.300

0.50 0.70 0.90 STI

33Acousteen, Herman Steeneken

Conclusions

• STI predicts the speech intelligibility for many

types of distortion: noise, band-pass limiting,

non-linearity's, temporal, vocoding, non-native

speech, and binaural hearing.

• Improvements (measuring methods or scope) of

STI will not change the qualification ranges.

• STI is an international standardized method

(ISO9921, IEC 60268-16) and used for many

national standards.