a presentation by dr. colin novak nvh-sq group university ... s2014/lecture 20 2014 92-455.pdf · a...

Introduction to Psychoacoustics and its Metrics

A presentation by Dr. Colin Novak – NVH-SQ Group

University of Windsor

Noise, Vibration, Harshness –Sound Quality Research Group

Copyright 2014 by Colin Novak. All rights reserved no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data

base or retrieval, without the prior written permission of the author.

Copyright ©2014, Colin Novak

OUTLINE

2

Noise, Vibration, Harshness – Sound Quality Research Group

• What is Sound Quality?

• Why improve the Quality of Sound?

• Noise vs. Sound

• Sound Quality Metrics

• Jury Testing or Subjective Tests

• Sound Quality Analysis Process

Lecture 20

Sound Quality

3


I like the

colour

200 HP!

It sounds

cool!

Lecture 20

Noise vs Sound

4


Noise

Measured:

to avoid hearing damage

to fulfill regulations

Measured as:

dBA

Sound Power

Sound

Perceived as:

pleasant sound

unpleasant sound

informative sound

Measured as:

“Sound Quality”

it sounds

bad

Power: 0.01 Watt

Lp = 88.5 dBA

LW = 100 dBA

Lecture 20

Why Improve Sound Quality

5


L = 63 dBA L = 63 dBA

Good Sound Quality signals proper operation of the product

Sound Quality is a parameter that sells the product

A-weighted noise levels and sound power are fine to characterize noise, but useless for sound

Sound Quality is not static, but changes over time like fashion

L = 63 dBA

Lecture 20

Click to Play

Example

Sound Quality Example

6


You will hear 5 refrigerator signals, all presented at the same time-averaged A-weighted sound pressure level.

Question: Would you find all of these refrigerator sounds equally desirable in your kitchen?

Lecture 20


7


Which refrigerator sound did you like the best?

Most people like refrigerator number 4 the best.

Did you? If not, why not listen again!

Click to Play

Example

Lecture 20


8


Using traditional SPL measurements for these signals, you can’t really see much relationship to your preferences.

SPL in dB(A) for Each Refrigerator

20

25

30

35

40

1 2 3 4 5

Refrigerator Number

SP

L in

d

B(A

)

Unweighted SPL for Each Refrigerator

20

25

30

35

40

45

50

55

60

1 2 3 4 5

Refrigerator Number

SP

L in

d

B

Lecture 20


9


Using Sound Quality metrics, it IS possible to measure differences in these signals which relate to your preferences! Here are just 4 such measures:

Max. Total Loudness

0

1

2

3

1 2 3 4 5

Refrigerator Number

Lo

ud

ness i

n s

on

es

Mean Total Loudness

0

1

2

3

1 2 3 4 5

Refrigerator Number

Lo

ud

ness i

n s

on

es

Percentile (N1) Instantaneous Loudness

0

1

2

3

1 2 3 4 5

Refrigerator Number

Lo

ud

ness i

n s

on

es

Refrigerator Number

Mean Zwicker Sharpness

0

1

2

3

1 2 3 4 5

Sh

arp

nes

s in

a

cu

m

Lecture 20

What is Sound Quality?

10


Having seen an example of a sound quality analysis what is the procedure to achieve these results?

Many manufacturers calculate simple models to predict how people will like their product sounds. These models are determined using either or both:

1) Sound quality metrics (i.e., objective measures) calculated with a sound quality software program, and/or

2) Jury Testing or Human preferences (i.e., subjective measures), determined by asking people to rate the product sounds.

Lecture 20

Sound Quality Metrics

11


“Zwicker Loudness”

Loudness is a measure of how “strong” a sound is to humans. That is, it

is a way of measuring a sound that corresponds to the subjective

perception of humans. This is very different than sound pressure, sound

intensity or sound power, which are physical quantities (remember the

refrigerator demo).

There are several methods or algorithms for determining loudness. The

Zwicker loudness method has been shown to have the highest

correlation to human perceived loudness. Zwicker loudness is a very

sophisticated algorithm and is used by most sound quality programs.

Lecture 20


12


Zwicker loudness can be used for 2 types of signals:

Stationary (“steady”) signals

• Starts with 1/3 octaves

• Linear averaging

• Uses frequency masking

• Computes 1 averaged loudness

spectrum

• Standardized measurement: ISO 532B /

DIN 45631

NonStationary (“non-steady”) signals

• Starts with 1/3 octaves

• Exponential averaging with time varying time

constants

• Uses frequency masking

• Uses time masking

• Computes a loudness waterfall

• Not standardized just yet.

Click for

Stationary

Signal

Click for

No stationary

Signal

Lecture 20


13


Typical stationary Zwicker loudness spectrum (ISO 532B):Curved line representsfrequency masking

Zwicker loudness is the

area under the curve.

(about 45 sones)

SpecificLoudnessaxis

Lecture 20


14


Typical Zwicker loudness waterfall plot of a nonstationary signal (a bell ringing after one hit): You get many loudness spectra, each spaced 2 msec apart!

Loudness non stationary spectrum

Original Signal

2 4 6 8 10 12 14 16 18 20 22 24

0

4

500m

1

1.5

2

2.5

3

3.5

[Bark]

[sone/Bark]

[s]

Loudness non stationary spectrum

Original Signal

2 4 6 8 10 12 14 16 18 20 22 24

0

4

500m

1

1.5

2

2.5

3

3.5

[Bark]

[sone/Bark]

[s]

Time

Lecture 20


15


Pleasantness

Annoyance

Tone-to-Noise Ratio

Prominence Ratio

Tonality, Pitch Strength

Speech Interference Levels (SIL)

Intelligibility, Articulation Index (AI)

Speech Transmission Index (STI)

Kurtosis

User Defined Metrics

etc.

Lecture 20

Jury Testing

16


Recording Analysis and Editing Playback

section section section

Lecture 20

Jury Testing

17


1. Original sound

2. Edited sound

3. Competitor’s

sounds

1 Play 2Subjective

Tests

Lecture 20

Objective

Test,

Metrics

Sound

Recording Subjective

Test

Product

Engineering

Trouble-shooting

Sound Quality Process

18


Sound

Quality

Program

Lecture 20

Sound Quality Process

19


What is Sound Quality?

Why improve the Quality of Sound?

Noise vs. Sound


Jury Testing or Subjective Tests

Sound Quality Analysis Process

Lecture 20

a presentation by dr. colin novak nvh-sq group university ... s2014/lecture 20 2014 92-455.pdf · a...

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