Multichannel Audio In Cars (Tim Nind)

Transcription

1 Multichannel Audio In Cars (Tim Nind) Presented by Wolfgang Zieglmeier Tonmeister Symposium 2005 Page 1

2 Reproducing Source Position and Space SOURCE SOUND Direct sound heard first - note different time of arrival and intensity at each ear Brain locates source direction in first few ms A Left Ear A Right Ear TIME INTENSITY t t Page 2

3 Early Reflections SOURCE SOUND Early reflections arrive from single boundary Reflected sounds provide distance cues and ambient information of space A Left Ear A Right Ear TIME INTENSITY t t Page 3

4 Late Reflections SOURCE SOUND Late arrivals come from multiple boundaries and decay with a specifc time envelope - reverberation Profile of time arrivals give sense of distance and space Time and intensity difference produces a natural soundfield A Left Ear A Right Ear TIME INTENSITY t t Page 4

5 Stereo Reproduction in a Room Page 5 Centre image is a phantom created by equal left and right signals Central listener hears central image Early and late reflections provide spatial cues Envelope of total sound power determines timbre combination of room and speaker Sense of ambience and envelopment dependent on room size and furnishings

6 Stereo Reproduction in a Room: Offset Listener Page 6 Centre image is biased to speaker closest to the listener as this is shortest time arrival and is a little louder HAAS effect Whole sound stage skewed to nearest speaker

7 Logic 7 System in the Home Developed for playback of 2 channel music by Lexicon SEVEN output channels derived from any 2 channel source Fully phase coherent in middle and back, stereo signal can be panned from front to rear Large sweet spot, excellent envelopment Page 7

8 Page 8 How Logic 7 Works Need to cope with signals varying from typical stereo to surround mix Lt Rt Continuously locates the loudest sound and calculates the steering vector (angle and magnitude) at each sample Depending on complex rules (instantaneous steering strength, history, type of music etc) directs corresponding control signals to the output matrix to determine the signal and gain of each channel Depending on the strength of steering smoothly transitions between the stereo default and full bandwidth steered signals, allowing 360 degrees of soundstage and full surround effect Full stereo separation is preserved from front to back The Lt Rt downmix (eg from Dolby Digital) provides best surround effect but normal 2 channel works well, particularly if recorded with natural or added reverberation

9 Logic 7 Decoders It is relatively easy to design a decoder which will work with a strongly steered signal, but such signals are rare. Music signals typically have very little net left/right loudness difference, but can move strongly from back to front. Logic 7 decoders maintain full stereo separation as the sound moves from the front to the back. Page 9

10 Music Reproduction in Cars Automobiles are different to listening rooms in significant ways and the playback should address these: The listeners are sitting significantly off centre The cabin space is too small for normal reverberation The playback space is divided into separate compartments by the two or three rows of seats The rear seat performance is more critical when RSE is fitted Multi channel source material is a bigger challenge as there are wide variety of ways the channels are used Page 10

11 Stereo Stereo Playback Playback in in Cars: Cars: Offset Offset Listener Listener Actual Panned Position Perceived Position Offset listener results in soundstage localised around nearest (left) speaker Page 11

12 Stereo Stereo Playback Playback in in Cars: Cars: Small Small Space Space Room is too small and absorbent to be able to generate much reverberant energy, resulting in little natural ambience Page 12

13 Stereo Stereo Playback Playback in in Cars: Cars: Logic Logic 77 Seven speaker architecture creates 360 degree soundfield 2 input channels processed to give 7 output channels Steered front sound stage and centre speaker puts performers where they should be Generated ambient signals recreate sense of space Rear door signal are special combination of front information and surround and make the rear seat performance as good as the front. Special steering for cars Rear steered signals provide great movie surround sound from RSE Page 13

14 Standard Standard 55 speaker speaker Architecture; Architecture; Phantom Phantom Centre Centre 5 channels are played back through 5 speakers typically with surrounds on rear shelf Front seat is usually ok unless the centre channel is not used in the production. There is nothing coming out of the centre speaker because there is nothing going in.this is quite common practice and results in a phantom centre, which is ok for a central listener but in a car the central performer is once again heard close to nearest speaker, just as in stereo. Page 14

15 Standard Standard 55 speaker speaker Architecture: Architecture: Poor Poor RSE RSE Rear seat is poor, with performers in front and typically only ambience or audience behind. Very dependent on the signals recorded in the surround channels RSE performance is very poor with dialogue in the front and audience or effects behind Page 15

16 Playback Playback in in Cars: Cars: Logic Logic 77 Multiseat Multiseat Listening Listening Seven speaker architecture creates 360 degree soundfield 5 channels processed to give 7 output channels Steered front sound stage puts performers where they should be, even if the centre channel is not used in the recording Rear seat performance as good as the front with performers in front of you and surround behind Page 16

17 Playback Playback in in Cars: Cars: Logic Logic 77 Excellent Excellent RSE RSE Seven speaker architecture creates 360 degree soundfield 5 channels processed to give 7 output channels Steered front sound stage puts performers where they should be, even if the centre channel is not used Rear seat performance as good as the front with performers in front of you and surround behind Excellent RSE experience with performers in rear of car and surround all around Page 17

18 Summary Discrete 5.1 multichannel audio is a significant differentiator in car audio but stereo material will be with us for the forseeable future and should not be ignored The car may be the most frequently used listening opportunity for 5.1 music Logic 7 systems provide a surround listening experience from stereo sources 5.1 signals require special processing to overcome the problems inherent in music reproduction in a car Logic 7 systems provide a multiseat listening experience and automatically compensate for variations in 5.1 material content Page 18