AES 116th, Workshop 14 The role of multiple low-frequency signals in - - PowerPoint PPT Presentation

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AES 116th, Workshop 14 The role of multiple low-frequency signals in - - PowerPoint PPT Presentation

May 26, 2023 163 likes •374 views

AES 116th, Workshop 14 The role of multiple low-frequency signals in the perception of reproduced sound Reproduction of low frequency effect and low frequency programme signal Gnther Theile theile@irt.de Low frequency reproduction A

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SLIDE 1

Reproduction of low frequency effect and low frequency programme signal Günther Theile theile@irt.de AES 116th, Workshop 14

„The role of multiple low-frequency signals in the perception of reproduced sound“

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SLIDE 2

Low frequency reproduction

A clear distinction

Low frequency effect (LFE) signal, carried over the separate low frequency extension channel. Separate radiation of low frequency programme content (LFP) through so-called subwoofers.

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SLIDE 3

L´ C´ R´ RS´ LS´ sub- woofer

5.1 surround recording

5.1 channels

Subwoofer: LFE (Low Frequency Effect) signal

L C R RS LS LFE

+10dB

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SLIDE 4

Low frequency separation

L´ C´ R´ RS´ LS´ sub- woofer

Σ

5.1 surround recording +10dB

LFE L C R RS LS

5.1 channels

Subwoofer: LFE signal plus LFP signal

LFP

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SLIDE 5

5.1 channels

LFE (Low Frequency Effect) signal

LFE is an option!

It can be used as a supplement for effects with extrem low frequency (20…80 Hz) and high level If not reproduced, it should not compromise the artistic integrity of the programme.

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SLIDE 6

ITU downmix matrix:

LO = L + 0,7*C + k*LS + 0*LFE RO = R + 0,7*C + k*RS + 0*LFE

Downward compatibility

5.1 surround 2-ch stereo

Also valid for the downmix Lt /Rt

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SLIDE 7

25 32 40 50 80 63 100 125 160 250 200 Hz

Low frequency reproduction

Another distinction 13 6,8 3,4 1,7 m

Low frequency fundament spatial/stereophonic information

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SLIDE 8

spatial/stereophonic information Low frequency reproduction

Test signal spectrum often used 25 32 40 50 80 63 100 125 160 250 200 Hz

„Low frequencies“?

13 6,8 3,4 1,7 m

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SLIDE 9

Low frequency reproduction

Demo: Band pass filtered (octave) pink noise 25 32 40 50 80 63 100 125 160 250 200 Hz 13 6,8 3,4 1,7 m

Low frequency fundament spatial/stereophonic information

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SLIDE 10

Surround Sound Forum

Alignment of reproduction equipment

Demo- and Test DVD www.tonmeister.de/foren/surround/dvd_order.html

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SLIDE 11

Subwoofer Loudness Subwoofer Loudness Please select the crossover-frequency of your playback device ! 80 Hz 100 Hz 120 Hz 160 Hz 200 Hz

Surround Sound Forum

Alignment of reproduction equipment

Demo- and Test DVD

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SLIDE 12

Subwoofer Loudness Subwoofer Loudness Please select the crossover-frequency of your playback device ! 80 Hz 100 Hz 120 Hz 160 Hz 200 Hz

Surround Sound Forum

Alignment of reproduction equipment

Demo- and Test DVD

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SLIDE 13

25 32 40 50 80 63 100 125 160 250 200 Hz

Surround Sound Forum

Alignment of subwoofer loudness 13 6,8 3,4 1,7 m

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SLIDE 14

80 Hz

Matching the subwoofer SPL

SPL Subwoofer = SPL Stereo-speakers

Applied to the crossover-frequency

Subwoofer Level Calibration

! Surround Sound Forum

Alignment of subwoofer loudness

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SLIDE 15

Low frequency reproduction

Crossover frequency: good compromise

25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz

L C R RS LS Subw.

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SLIDE 16

Low frequency reproduction

Crossover frequency: too high

25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz

L C R RS LS Subw.

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SLIDE 17

Low frequency reproduction

Crossover frequency: best choice!

25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz 25 32 40 50 80 63 100 125 160 250 200 Hz

L C R RS LS Subw.

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SLIDE 18

Low frequency reproduction

Subwoofers

Low frequency separation:

  • Crossover frequency should not exceed about 60…80 Hz

and should be as low as possible

  • One monophonic LFP signal is sufficient, however,

two subwoofers instead of one can be advantegeous (see e.g. Todd Welti)

  • Crossover frequency and number of subwoofers are a

compromise between loudspeaker cost and design, „household compatibility“ and sound quality

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SLIDE 19

Low frequency reproduction

Low frequency effects

LFE signal:

  • There is no technical reason for the LFE channel, it is

just a supplementing „low frequency fun“ channel

  • If not reproduced, it should not compromise the

artistic integrity of the programme

  • Frequencies > 80 Hz carry spatial/stereophonic

information and thus programme content It should be used only for effects with extrem low frequency (20…80 Hz) and high level A second LFE signal below 80 Hz has no spatial effect and thus is useless

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SLIDE 20

Low frequency reproduction

Conclusion

Any low frequency spatial audio effect can be and should be achieved without extra LFE fun channels. If the listener wants to perceive best spatial audio quality, he has to invest a loudspeaker / subwoofer setup with crossover lower than 80 Hz. Supplementing highest level low frequency vibration effects should be allocated to the LFE fun channel, in order to keep the artistic integrity of the programme untouched and to allow easy turning-off. For some recordings without supplementing LFE effects the provision of a lower level LFE dummy signal avoids an empty .1-channel and thus disappointed customers.