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		+	=====speech transmission index=====
		+	Speech transmission index (ger. Sprachverständlichkeit) is a number between 0 an 1 representing the normal human ability to understand the contents of a spoken message based on sound properties. 0 represents a bad STI, 1 represents best STI. Derivates of the STI are RASTI (rapid speech transmission index) and STIPA (STI  public address - a spezialized selection of representative data for public address applications).
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Revision as of 08:49, 27 March 2008

Jump to: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Contents 1 A 1.1 absolute pitch 1.2 adaptation 2 B 2.1 bandwidth 2.2 band power level 2.3 band pressure level 3 C 3.1 cut-off-frequency 4 D 4.1 decacy time 5 E 6 F 6.1 forward masking 7 G 8 H 9 I 10 K 11 L 12 M 13 N 13.1 neper 13.2 nominal bandwidth 14 O 15 R 15.1 reverberation 15.2 reverberation time 16 S 16.1 speech transmission index 17 T 18 U 19 V 20 W 21 Z 22 References

A

absolute pitch

Absolute pitch (ger. Absolutes Gehör) is the ability to identify the musical note (frequency) of a clear sine tone without an external reference.

• Remark: The allowed variance has to be defined.
• Remark: Mostly a musical note is identified not a frequency value.

adaptation

Adaptation (ger. Adaption) ...

B

bandwidth

The nominal bandwidth (ger. Bandbreite) of a filter is given by the difference between the upper and the lower cut-off-frequency. This difference may be expressed (1) in Hertz, (2) as percentage of the center frequency of the pass-band or (3) as the interval defined by the upper and lower cut-off-frequency in octaves (i.e. 1 octave, 1/3 octave)

• Remark: For more definitions see also USA Standard Method for Specifying the Characteristics of Analyzers Used for the Analysis of Sounds and Vibrations, Z24.15-1955

band power level

The band power level (ger. Band-Leistungspegel) of a sound for a specific wave band is the sound power level of a sound within a limited wave band.

band pressure level

The band pressure level (ger. Band-Schallpegel) of a sound for a specific wave band is the sound pressure level of a sound within a limited wave band.

• Remark: The wave band may be specified by its lower and upper cut-off-frequency or by its pass-band and the bandwidth. The bandwidth of the band may be specified as follows: octave-band (sound) pressure, half-octave-band pressure, third-octave-band pressure, 50-Hz-band pressure.

C

cut-off-frequency

The cutoff frequency (ger. Grenzfrequenz, Eckfrequenz) is the frequency nearest to the center frequency where the level exceeds ±3dB.

D

decacy time

decay time (ger. Abfallzeit) In general it is the time between a sound pressure level and a lower sound pressure level. Both levels have to be defined explicitly. It is also useful to describe the decay time as speed of lowering sound pressure level (db/sec).

• Note1: The decay time constant characterizes the exponential decacy of sound after stopping the sound source (Unit: s^-1).
• Note2: If p₀ is the effective sound pressure after stopping the sound source at t = 0 and p(t) is the effective sound pressure level at t, and p(t) = p₀*e^-k*t is imperative, then k is the decay constant.

E

F

forward masking

(ger. Nachverdeckung): see also "masking".

G

H

I

K

L

M

N

neper

Neper (Np) (ger. Neper) is a unit used to express ratios, such as gain, loss, and relative values.

• The neper is analogous to the decibel, except that the Naperian base e (2.718281828...) is used in computing the ratio in nepers.
• The value in nepers, Np, is given by Np = ln(x1/x2), where x1 and x2 are the values of interest, and ln is the natural logarithm, i.e., logarithm to the base e.
• One neper (Np) = 8.686 dB, where 8.686 = 20/(ln 10).
• One dezibel (dB) = 0.1151 Np, where 0.1151 = ln(10)/20.
• The neper is often used to express voltage and current ratios, whereas the decibel is usually used to express power ratios.
• Np is a dimensionless unit (like dB).
• The ITU recognizes both units.

nominal bandwidth

See bandwidth

O

R

reverberation

Reverberation (ger. Nachhall) is all sound due to reflexions measured in a closed system (room) after the sound source has stopped activity.

reverberation time

The reverberation time (ger. Nachhallzeit) is defined as the time needed the sound level reaches -60dB of average active sound level after stopping the sound source.

S

speech transmission index

Speech transmission index (ger. Sprachverständlichkeit) is a number between 0 an 1 representing the normal human ability to understand the contents of a spoken message based on sound properties. 0 represents a bad STI, 1 represents best STI. Derivates of the STI are RASTI (rapid speech transmission index) and STIPA (STI public address - a spezialized selection of representative data for public address applications).

T

U

V

W

Z

References

• [ANSI] American National Standard Psychoacoustical Terminology (1973): ANSI S3.20-1973; Approved December 5, 1973; American National Standard Institute, Inc.
• [YOST] Yost, William A. & Donald W. Nielsen (1977): Fundamentals of Hearing. An Introduction. Holt, Rinehart and Winston; New York.