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

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 Günther Theile theile@irt.de

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.

5.1 channels Subwoofer: LFE (Low Frequency Effect) signal L´ L C´ 5.1 surround recording C R´ R RS RS´ LS LS´ sub- LFE +10dB woofer

woofer sub- RS´ LS´ C´ R´ L´ Low frequency Σ Subwoofer: LFE signal plus LFP signal separation LFE LFP RS LS C R L +10dB 5.1 channels 5.1 surround recording

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.

Downward compatibility 5.1 surround � 2-ch stereo ITU downmix matrix: L O = L + 0,7*C + k*LS + 0*LFE R O = R + 0,7*C + k*RS + 0*LFE Also valid for the downmix � L t /R t

Low frequency reproduction Another distinction spatial/stereophonic information Low frequency fundament 25 32 40 50 63 80 100 125 160 200 250 Hz 13 6,8 3,4 1,7 m

Low frequency reproduction Test signal spectrum often used spatial/stereophonic information „Low frequencies“? 25 32 40 50 63 80 100 125 160 200 250 Hz 13 6,8 3,4 1,7 m

Low frequency reproduction Demo: Band pass filtered (octave) pink noise spatial/stereophonic information Low frequency fundament 25 32 40 50 63 80 100 125 160 200 250 Hz 13 6,8 3,4 1,7 m

Surround Sound Forum Alignment of reproduction equipment Demo- and Test DVD www.tonmeister.de/foren/surround/dvd_order.html

Surround Sound Forum Alignment of reproduction equipment Demo- and Test DVD Subwoofer Loudness 80 Hz Subwoofer Loudness 100 Hz 120 Hz Please select the crossover-frequency of 160 Hz your playback device ! 200 Hz

Surround Sound Forum Alignment of reproduction equipment Demo- and Test DVD Subwoofer Loudness 80 Hz Subwoofer Loudness 100 Hz 120 Hz Please select the crossover-frequency of 160 Hz your playback device ! 200 Hz

Surround Sound Forum Alignment of subwoofer loudness 25 32 40 50 63 80 100 125 160 200 250 Hz 13 6,8 3,4 1,7 m

Surround Sound Forum Alignment of subwoofer loudness Subwoofer Level Calibration Matching the subwoofer SPL ! SPL Subwoofer = SPL Stereo-speakers Applied to the crossover-frequency 80 Hz

Low frequency reproduction Crossover frequency: good compromise L 25 32 40 50 63 80 100 125 160 200 250 Hz R 25 32 40 50 63 80 100 125 160 200 250 Hz C 25 32 40 50 63 80 100 125 160 200 250 Hz LS 25 32 40 50 63 80 100 125 160 200 250 Hz RS 25 32 40 50 63 80 100 125 160 200 250 Hz Subw. 25 32 40 50 63 80 100 125 160 200 250 Hz

Low frequency reproduction Crossover frequency: too high L 25 32 40 50 63 80 100 125 160 200 250 Hz R 25 32 40 50 63 80 100 125 160 200 250 Hz C 25 32 40 50 63 80 100 125 160 200 250 Hz LS 25 32 40 50 63 80 100 125 160 200 250 Hz RS 25 32 40 50 63 80 100 125 160 200 250 Hz Subw. 25 32 40 50 63 80 100 125 160 200 250 Hz

Low frequency reproduction Crossover frequency: best choice! L 25 32 40 50 63 80 100 125 160 200 250 Hz R 25 32 40 50 63 80 100 125 160 200 250 Hz C 25 32 40 50 63 80 100 125 160 200 250 Hz LS 25 32 40 50 63 80 100 125 160 200 250 Hz RS 25 32 40 50 63 80 100 125 160 200 250 Hz Subw. 25 32 40 50 63 80 100 125 160 200 250 Hz

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

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

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.