Co-presented by DTS, Genelec, Soundfield, Steinberg and Real Traps
at the 117 ^th AES Convention

When our friends at DTS offered to fly me to San Francisco to cover a seminar they were putting together, I was intrigued. From it's somewhat generic sounding title I was at a loss to figure out how this seminar presentation would play out.

Real Traps, a room acoustics company who have made a name for themselves in tweaking out recording studios were not mentioned in the initial press releases to this seminar so the only other company with which I had great familiarity was Genelec ., one of the most respected powered-studio monitor speaker suppliers to the professional industry.

Imagine my delight then when it became apparent that DTS, a supplier of high resolution decoding algorithms, had taken on the somewhat formidable task of teaching a complete nuts-to-bolts approach to recording and studio design which, fastidiously followed, would allow a recording engineer or producer to hear and thus maximize DTS' high resolution capabilities in the prescribed recording environment. And in only 1 ½ hours no less!

Well, the bad news is that such a task, utilizing 5 presenters speaking for only minutes each, could cover only very basic concepts or explanations of their products. The good news is presented here. DTS' Rodney Orpheus, who records out of a 400 year-old Elizabethan manor in England, was gracious enough to chase down the slides used by each of the 5 presenters for each of their presentations so it could all be reassembled here.

Most times when evaluating a recording, most of us have no idea how much manipulation (or lack thereof) took place in preparing that recording for sale. We have no way of knowing what the room acoustics were, the monitors used, the microphones, the mixing console or the numerous black boxes through which the signal passed until it reached a final encoder such as the Steinberg SP451 Surround Sound Processor whose embedded Nuendo software carries the DTS encoding algorithms.

After reading the details of this seminar which follow, perhaps a greater perspective can be had as to how the mover's and shakers in the recording industry are reconfiguring their recording studios and DAWs (digital audio workstations) for surround. New tools are also required for surround, and are being made available by innovative companies such as Soundfield . Their single-microphone solution to recording stereo and surround is fascinating in both its design ingenuity and awesome capture of surround information…let's start from the beginning…

Real Traps was the first presenter and it is interesting to note that they affix their own subtitle to the main Understanding Studio Production theme. That subtitle was " The Importance of Acoustic Treatment in Music Production " (The underline of "music" is mine.) Also of interest, to me at least, was the fact that, like consumer audio, the pro audio guys are slow to adapt to some of the newer, proven methods of controlling bass in a room. The use of 1/12 ^th octave minimum, single-band parametric EQing of subwoofers in the room is not yet mentioned. Instead, longer- recognized methods of controlling bass are recommended. From Real Traps slide set:

Useful Guidelines

• All rooms need acoustic treatment for:
  - Bass trapping at the lowest frequencies possible, for a tight low-end
  - Control of first reflections for mid/high frequency imaging
• The smaller the room, the more low frequency absorption is needed:
  - Reflections are greater in amplitude
  - Modes are fewer and spaced further apart
• Especially relevant for the trend in ever-smaller production rooms
• As best we can determine, you can't have too much bass trapping..if …your bass traps are designed properly

The Ideal Bass Trap

• Substantial absorption to as low a frequency as possible including those well below 125 Hz.
• Absorption that decreases at the higher frequencies (above 200 - 300 Hz)
• Easy to mount and move (transportable)
• Comes in convenient sizes to accommodate room geometries
• Optional stand for floor mounting
• Class A Fire Rated for safety in public and private venues.

Understanding Surround Sound Production - page 2

Next up was Genelec. Their segment of the presentation was entitled " Active Monitoring for Multichannel Audio " with the subtitle " Monitors, Monitor Set-up, LFE Channel and Bass Management ". Professionals that they are, Genelec started by pointing out:

Important International Recommendations (and committee networking relationships)

• AES Technical Committee is working with EBU and SMPTE
• German Surround Sound Forum (SSF)
• ITU works with IEC, SMPTE and ISO/MPEG Committee
• ITU-R BS.775-1 "Multichannel stereophonic sound system with and without accompanying picture" (Geneva, 1992-94)
• ITU-R BS.1116-1 "Methods for the subjective assessment of small impairments in audio systems including multichannel sound systems" (Geneva, 1994-97)

Subwoofer in the Control Room

• Very low frequencies provide minimal audible localization cues
• One or more subwoofer(s) can be used
• Very useful to check the LF signal that is sent with program

Placement:

• Close enough to the front wall to give efficient loading ( < 0.6m)
• Offset from the symmetry axis of the room to avoid lateral standing waves minima
• In a corner, close to both front and side walls
• Flush-mounting of subwoofer(s) possible

Subwoofer Adjustment Needed:

1. Gain, to adjust for the radiation loading
2. Frequency response
3. Phase adjustment, at the crossover point

The LFE Channel

• LFE channel comes from the movie theater productions
  L ow F requency E nhancement
  L ow F requency E ffects
• Practical use of the LFE channel is not consistent
• The multichannel mix down is done to 6 or 7 discrete tracks
• All tracks are identical on the recording media-one of these tracks is labeled 'LFE channel'
• The LFE channel before encoding is NOT band limited (full bandwidth)

How to Monitor the LFE Channel?

• The subwoofer response is acoustically aligned at the same level as the main channels
• LFE channel is only monitored at +10dB (Dolby Digital, DTS)
• Thus, LFE is given 10dB additional headroom going to tape

It is important to understand the significance of this slide. The 120Hz LFE upper cut-offs listed for all Dolby and DTS are the original recommendations from the two companies . However, to my knowledge, all Dolby and DTS chipsets installed in consumer receivers and pre/pros roll the LFE channel off at 80Hz in the software.

Therefore, if you're running a 5 or 7 satellite-with-subwoofer system wherein the satellite is not capable of going down to 80Hz, you are losing all the information (musical or otherwise) from 80Hz to your satellite's low frequency cut-off point when listening/viewing to Dolby Digital or DTS sources. The loss of these frequencies, typically from 80Hz up to 150Hz or even 200Hz for tiny cube-style satellites is definitely audible once a more capable (of lower frequency response) satellite is substituted.

Similarly, if you like to listen to two-channel sources on your two-full range left and right tower speakers, augmented by a subwoofer with a fixed-at-the-sub roll-off of, say, 40Hz… when you switch back to watch a Dolby or DTS DVD your system would have a hole in it from 40Hz to 80Hz. This hole is much harder to hear given the ears' insensitivity to missing bass frequencies.

Understanding Surround Sound Production - page 3

The Genelec Demo System

The above slides represent the monster system Genelec set-up for the demo. Pay particular attention to the included pictograms to the right on each of these slides. On them you will note the recommended room sizes, distance to listening position, low frequency cut-off, maximum SPL, etc. Note also the transducer complement of each system along with the amplifier to which the transducers are coupled. Finally, the tone control section shows the Genelec's system tuning flexibility once they are installed. Usually, these controls are set during initial calibration and not touched thereafter.

The Soundfield Microphone Array
Soundfield's approach to capturing both stereo and surround sound is truly ingenious. The goal in designing the Soundfield microphone array was to accurately and realistically capture a three-dimensional audio experience.

Based on a patented multi-capsule array each of the four capsules in the array pick up sound from a different direction. It is this information which is used to capture a soundfield. The four signals from the capsules are collectively named A-Format. Once the signals are captured they go through one of three available Soundfield control unit models which convert the signals into a proprietary Soundfield B-Format.

After the SoundfieldB-Format is recorded onto four tracks, this information can be decoded into any required audio format: mono, stereo, M/S, 5.1,6.1,7.1 or any custom multi-speaker playback system.

In addition to the three stand-alone control units Soundfield has also introduced the Surround Zone which is a software plug-in available for Nuendo (Steinberg), Cu base, SADIE 5 and shortly, ProTools.

And Finally…DTS!
Rodney Orpheus, DTS' European Entertainment Manager, gave some very interesting statistics and introduced DTS' patented technologies which will take them into the future.

• Worldwide, more than 280 million consumer electronics products containing DTS technology and trademarks have been licensed: these include-
• DVD players, A/V receivers, amp/pre-amps, HTIB
• Playstation®2 game consoles (70+ million units)
• In-car audio processors and head units
• PC-based software decoders and PC soundcards

And the technology? Well, the Eagles classic "Hell Freezes Over" stands as the first, great DVD concert recording I've ever owned. It came in the original DTS Digital Surround format way back in 1994. I've been a fan of DTS' natural sounding algorithms ever since. It's hard to know what else to say about a technology which is so transparent that I can't detect that any processing or compression is taking place.

Let me put it this way. By the time I'm voicing a speaker system which I've designed from the ground up, I've got a pretty good idea of the ultimate capabilities of the drivers, in the given box, with the chosen crossover configuration. The (usually) ported design and cabinet bracing are taken care of as listening begins. After this step, the sound begins to converge closer and closer, toward its ultimate capabilities, Then I'm making tiny changes to the crossover components, all the while rechecking (by measurement) that I'm maintaining the frequency balance and (flat) response that is my target.

At the end, I experience the sound "locking". The woofer, tweeter, enclosure and crossover all converge to give a sound that is at once natural, smooth, easy to listen to but accurate and non-hyped. This is the sound I hear with a great recording in the DTS Digital Surround format. I hear the music, not the format. That's what I call a great technology.

Rodney's demonstration of DTS' 96/24 with 5.1 channels of high resolution audio and full motion video were followed by and a clip from Lord of the Rings in ES 6.1.

And lastly, the teaser. DTS HD has been chosen as a mandatory format when high definition DVDs are introduced sometime next year. Audioholics will be there to review DTS HD's sound quality as soon as the first products become available. Perhaps at the 2005 CES…