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An Interview with Dr. David Griesinger, by Philip Brandes
Part One

Dr. David Griesinger is one of the world's foremost authorities on surround psychoacoustics and sound engineering. As chief scientist for Lexicon, Inc., since the 1980s Dr. Griesinger has designed and developed the company's proprietary surround processing algorithms, which are used in such diverse applications as pro audio gear for recording studios, concert hall acoustical design, venue simulation systems for musician rehearsal, and a successful consumer line of home surround preamp/processors.

Dr. David Griesinger

In the home audio/video field, Dr. Griesinger is best known as the architect of Lexicon's Logic 7 processing.

A collection of his professional publications and presentations can be found on his website at In a recent interview, Dr. Griesinger spoke with SMR reporter Philip Brandes about some of the history and science behind Lexicon's Logic 7 and Bass Enhance processing, as well as future trends in home theater surround technologies.

PB: Based on your published work and Lexicon's prominence in the pro audio world, your priorities seem geared more towards music first, and home theater as a byproduct.

That's absolutely true. I started out as a recording engineer, recording classical music concerts. Well, I'm officially a nuclear physicistI have a degree in atomic nuclear physics. I worked my way through graduate school as a recording engineer doing classical music and so forth. That was my passion. And when I got through with my PhD, I went to work immediately on digital reverberation. Working as a recording engineer, I knew the most important thing that nobody had was good reverb, and I thought maybe I could make it. So I've done that ever since.

The Logic 7 system came out of movies, though. I built our first matrix system at the request of Rene Jaeger, who is in my opinion one of the audio greats, but a very quiet guy who doesn't toot his own horn. Originally he was one of the founders of DBX, and I was able to lure him away and he spent ten years as a project manager at Lexicon. Though I was more involved with Lexicon's Pro audio products, he dragged me kicking and screaming into the consumer world and told me to make a film decoder. So I did.

PB: What isn't generally known about Logic 7 is that it's an encode format as well as a playback format. One of the coolest features of the Lexicon pre/pros is their ability to downmix 5.1 recordings to Logic 7-encoded two-channel.

Yes, we can take a surround recording and turn it into a 2-channel recording with the encodercompletely automaticallyand play it back with really good results in surround. [The terms 5:2:5 and 5:2:7 are used to describe this process of downmixing a 5-channel recording to matrix-encoded 2 channels, then decoding it for playback in 5 or 7 channelsP.B.]

If the recording is good originally, and you play [someone] the discrete version and then have them walk out of the room and then switch to the 5:2:5 or 5:2:7 matrix version, then walk back in the room, they won't know which is playing. If you sit there and A/B them, you'll get a good idea which one is playing after a couple of shifts, but it's really quite close...and often the matrix one sounds better.

PB: Better? It seems counterintuitive to suggest that matrix decoding can sound better than discrete.

The reason for that, I think, is that most music mixers are only beginning to learn how to really use that medium and frequently they don't treat the reverberations as well as they might. Instead, they mix things a little too discretely.

If you take it down to two channels, then take it back up seven, or five, it really makes it more pleasant in some ways. That's not true of the very best recordings; if you go down to two channels and back to five there is some loss. There's no question that 5:2:5 is a lossy system. It's not lossy in the sense of an encoding scheme with artifactsyou don't lose anything from the apparent quality of the discyou lose aspects of spatial placement, which are often more subtle. You can find discrete material that doesn't work very well in a downmix, it's just that that material is not common.

PB: What kind of material might exceed the capabilities of a matrix-based algorithm?
DG: I did a multimedia show recently for a group that wanted a very complicated presentation over 7 channels in one of these round theaters where the dialog came from all directions and there were sound effects coming from all directions at the same time. It was very complicated, and I couldn't make that work to my satisfaction in 5:2:7. They would have loved it, and I think they actually use it anyway. But to me, the presence of strong sound effects off in the left rear can tend to move the dialog a little bit. If the dialog is in a place like the left there can be kind of a shifting of the dialog position which is really noticeable, and the discrete system in that case really was in my opinion superior, because it locks everything where you put it, and a matrix system simply can't do that. But if your goal is ambience it produces it as well as anything else. Well, actually that's not entirely trueI've been studying that problem recently in some detail and I know that the matrix system does very well in some frequency bands and maybe not so well in others. But again it's very hard to tell the difference except in very specific cases.
PB: Since Logic 7 is compatible with Pro Logic matrix decoders, some engineers are using it to re-master the Dolby Surround mixes for major DVD releases like 'Se7en' and 'The Cell'. Has any thought been given to promoting Logic 7 as an encode format?
DG: Most of the big players aren't interested. The "Not invented here" syndrome is a big factor. Mostly, it's just not in their own interests. What we're offering is a way of making ordinary 2-channel recordingsof which the average consumer probably has hundreds alreadysound really fairly decent in surround. This is not exactly in record companies' interest if they're wanting to get the consumers to buy a whole new record library of surround recordings, or if they're thinking along the lines of taking their old master tapes, remastering them in surround, and offering them that way. The record companies really want to have some way of selling stuff to a much wider audience, and now that everybody has a lot of CDs, they need something new--and a technology that allows you to play the old with very good results in a new format isn't something that they really want to jump at. I can't say that anyone has ever actually resisted it or tried to throw up roadblocks, they're just not interested. So you get players like Sony and Philips and Warner who are really going their own way.
PB: How is Logic 7 different from THX Surround EX, and DTS ES, which also use two additional rear speakers?

If you take our setup and set it to 5.1 Logic 7, which is a 5-channel to 7-channel matrix, it's quite different from EX. I think the difference is really quite dramatic. If you have 4 rear speakers in a 7-channel system and you switch from Logic 7 to EX, the rear speakers switch from stereo to mono, and it's really quite audible. I think that's unfortunate, but then again it's very definitely a "Not invented here" kind of thing. They looked at my circuit and said Griesinger has this, what can we do that's different?"

Now the 6-speaker setuptwo at the sides and one in the middle behind youreally doesn't work very well. And that's the arrangement [originally] chosen for Dolby EX, but I think that they just didn't do their homework.

PB: They're still using two speakers, but it's mono....they're only licensing 2 speakers in the rear for THX Ultra products (1 speaker in the rear for THX Select)...
DG: They've changed their tunebut that wasn't true a year ago when I first started working on it.
PB: So the trade-off is between Logic 7's matrix derived stereo rears versus the EX mono rear content specified by the recording engineer.

Yes. There's no question [stereo rears] are more involving. And as I said, most music mixers are only beginning to learn how to really use the medium.

PB: Are you continuing to evolve Logic 7?
DG: Oh, yeah, definitely. Right now, I'm not working on it in the home, I'm working on it in automobiles, but several of the [new] things I've found that work very well in that environment will definitely work in the home.
Go To Part Two

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