LTSPICE AUDIO SIMULATION:

A LOUDNESS CONTROL

Bee Technologies Inc.

20AUG2012

1

EQUAL-LOUDNESS CONTOUR

Equal-loudness contour is a measure of sound pressure (dB SPL), over

the frequency spectrum, for which the human ear perceive the same

loudness when presented with pure steady tones (unit is the phon).

For more info . . .

http://www.sfu.ca/sonic-studio/handbook/Equal_Loudness_Contours.html

40

60

80

100

120

10 100 1000 10000

INT

EN

SIT

Y L

EV

EL

(d

B)

FREQUENCY (Hz)

100

90

80

70

60 Loudness level (phon)

Contours of equal loudness (from the Radiotron Designers Handbook).

2

A LOUDNESS CONTROL

A loudness control is used as an attempt to restore extreme low and high

frequencies. As the sound level decreases, the ear becomes less sensitive

to both extreme low and high frequencies. Thus, when listening at reduced

levels, if the frequency response of your system is maintained flat, you will

not hear those extremes as well.

C176.9739p

PARAMETERS:

RVOL = 500k

VOL = 0.0245

PARAMETERS:

RVOL1 = {(1-VOL+1u)*RVOL}

RVOL2 = {(VOL+1u)*RVOL}

RVOL-2

{RVOL2}

RVOL-1

{RVOL1}

Output

V11Vac

0Vdc

Input

0

R1

200k

0

C258.7883n

R22.2119meg

R3330

R42MEG

L120m

1

2

R5

4.6695k

C3

3.9244n

Frequency

100Hz 1.0KHz 10KHz20Hz 50KHz

DB(V(OUTPUT))

-60

-40

-20

0

20

DB(V(OUTPUT))

A loudness control and its frequency response (example)

3

THE LOUDNESS CONTROL VS. EQUAL-LOUDNESS CONTOUR

-60

-40

-20

0

20

10 100 1000 10000

INT

EN

SIT

Y L

EV

EL

(d

B)

FREQUENCY (Hz)

100

100(Sim)

90

90(Sim)

80

80(Sim)

70

70(Sim)

60

60(Sim)

Frequency response of the loudness control (simulation) is compared to the equal-loudness contour.

4

Loudness Control vs. Flat Volume

C176.9739p

PARAMETERS:

RVOL = 500k

VOL = 0.0245

PARAMETERS:

RVOL1 = {(1-VOL+1u)*RVOL}

RVOL2 = {(VOL+1u)*RVOL}

RVOL-2

{RVOL2}

RVOL-1

{RVOL1}

Output

V11Vac

0Vdc

Input

0

R1

200k

0

C258.7883n

R22.2119meg

R3330

R42MEG

L120m

1

2

R5

4.6695k

C3

3.9244n

C176.9739p

PARAMETERS:

RVOL = 500k

VOL = 0.0245

PARAMETERS:

RVOL1 = {(1-VOL+1u)*RVOL}

RVOL2 = {(VOL+1u)*RVOL}

RVOL-2

{RVOL2}

RVOL-1

{RVOL1}

Output

V11Vac

0Vdc

Input

0

R1

200k

0

C258.7883n

R22.2119meg

R3330

R42MEG

L120m

1

2

R5

4.6695k

C3

3.9244n

LOUDNESS CONTROL FLAT VOLUME

The High-Pass

circuit is

disconnected, the

Low-Pass circuit

is short to ground

5

Frequency

100Hz 1.0KHz 10KHz20Hz 50KHz

DB(V(OUTPUT))

-60

-40

-20

0

20

Frequency

100Hz 1.0KHz 10KHz20Hz 50KHz

DB(V(OUTPUT))

-60

-40

-20

0

20

DB(V(OUTPUT))

Loudness Control vs. Flat Volume

LOUDNESS CONTROL RESPONSE FLAT VOLUME RESPONSE

6

LTspice Simulation: .WAV IN/OUT Loudness Control

Loudness Control with .WAV input and output Simulation result: input and output signal

Low to high swept audible signal (Input)

-30 dB level down with the loudness control (Output)

7

LTspice Simulation: .WAV IN/OUT Flat Volume

Flat Volume with .WAV input and output Simulation result: input and output signal

Low to high swept audible signal (Input)

-30 dB level down with the flat volume (Output)

8

.WAV FILES LOCATION

An input file Output files created

by LTSpice

9

USING WAVE FILE (.WAV) AS INPUT

Using audio signal (WAVE file) as an input voltage for LTSpice could be done

by replace the voltage expression of the voltage source with a WAVE-file

expression: wavefile=“file location" chan=0 (as seen in the example

below)

“chan” refers to the respective channel in the WAVE file used for the

simulation, can be a number between 1 and 65535 although usually

channel 0 refer to the left channel and channel 1 refers to the right channel

A loudness control and its frequency response (example)

10

USING WAVE FILE (.WAV) AS OUTPUT

Exporting an output signal as an audio signal (WAVE file) could be done by

adding SPICE directive as: .wave=“file location" 16 44100 Output (as

seen in the example below)

“16” refers to the bitrate, 44100 is the sampling frequency and Output is

referring to a label in circuit.

A loudness control and its frequency response (example)

11

LTspice Simulation: music01.WAV IN/OUT Loudness Control

Loudness Control with music01.WAV input and output Simulation result: input and output signal

music01.wav audio signal (Input)

-30 dB level down with the loudness control (Output)

12

LTspice Simulation: music01.WAV IN/OUT Flat Volume

Low to high swept audible signal (Input)

-30 dB level down with the flat volume (Output)

Flat Volume with music01.WAV input and output Simulation result: input and output signal

13

.WAV FILES LOCATION

An input file

Output files created

by LTSpice

Output files created

by LTSpice

14

VIDEO DEMONSTRATION

15