Sunday, January 17, 2010

How Does Surround Sound Work

Sound All Around
Surround-sound audio requires more than just two speakers to get it right. Several speakers are placed in various areas of a room to achieve a fully rounded sound quality. The audio connector is split so that multiple connections can be made easily.
Left and Right Audio
As in most stereo televisions, there should be a speaker to the left of the screen and another to the right, picking up sounds from the corresponding parts of the screen. The left and right speakers pick up the most common and best-defined sounds from the audio track, splitting them perfectly in half so you hear the action coming from two locations at once.
Third Speaker
Unlike most stereo speaker systems, in surround sound you have a third speaker in-between the left and right speakers. This speaker gives you the dialogue and sound effects that are featured front and center on the screen, the prominent features of the broadcast or video. This makes it seem as though you are hearing everything from left, right and center equally powerfully.
Background Speakers
You will hear whatever is going on in the background of the movie or television show from the speakers positioned behind you. This makes it seem like you are right in the center of all the action, almost as if you are starring in the feature yourself. If a sound enters the screen from the distance, you will hear it behind you first. As it passes by, you will hear it more toward the front speakers. For example, a jet passing overhead really sounds like a jet passing overhead.

9/11 Fahrenheit


STROTHER BULLINS talks to Skywalker Sound's Gary Rizzo about his dual role as Supervising Sound Editor and Sound Re-recording Mixer for the most commercially successful documentary in history, Fahrenheit 9/11.
Sound Editor and Re-recording Mixer Gary Rizzo is no newbie to documentaries or - as he prefers to call them - 'non-fiction' films. After years of working on a variety of well-received IMAX and various other documentaries alongside massive Hollywood blockbuster-style feature films, Rizzo was tapped to serve dual roles as both Supervising Sound Editor and Re-recording Mixer for what has become the most successful documentary in history, Director/Producer Michael Moore's riveting and controversial Fahrenheit 9/11.
"In terms of standard documentary films, none that I have done before have been as commercially successful or as popular as Fahrenheit 9/11," understates Rizzo. "I can't say that I had an extraordinary amount of background in non-fiction work, but I did have enough to feel comfortable with getting involved in something like this, and I certainly didn't approach it with any fear."
Winner of the Palme d'Or at the 2004 Cannes Film Festival, Fahrenheit 9/11 has proved to be a film simultaneously loved and hated, divisive and unifying, critical yet hopeful. The film critically examines United States President George W. Bush's methods of handling of the September 11, 2001, terrorist attacks.
Gary Rizzo, approached the job without "any fear"
"If the success of Fahrenheit 9/11 opens up more opportunities for documentaries to be seen and opinions to be shared, it's nothing but a good thing for everyone," reasons Rizzo. "At the time, we had no idea how successful it would end up being."
A Better View
While Rizzo readily admits that serving as both Supervising Sound Editor and Sound Re-recording Mixer on Fahrenheit 9/11 was a lot of work, it also gave him a better view of what Moore envisioned his film to be. "In the film world, those two jobs are generally separate," he explains. "One person takes care of the editorial of the sound and another person mans the mix. I don't mind doing both, and actually, I kind of appreciate it. The more time you spend with the project editorially and the more time you spend with the director in an atmosphere where you are building and constructing the tracks, the better view you have of the project from the director's eyes. You simply have better opportunities to figure out exactly what the director is trying to accomplish with the sound."
Michael Moore (right) and Sgt. Abdul Henderson on Capitol Hill attempting to convince congressmen to send their sons to Iraq.
After Rizzo accepted the dual role job, Sound Editor Scott Guitteau was promptly invited to join the sound team. "I hired a dear friend of mine who is - well - definitely on the left side of things," chuckles Rizzo. "I knew that he was the perfect guy to work with me on this, based on his political views and the creative input that he would bring to the project. Between the two of us, we took care of the entire sound/post-production track."
Working At A Rapid-Fire Pace
Rizzo and Guitteau began work on Fahrenheit 9/11 at Skywalker Sound, but after only two weeks they moved to Moore's New York office for approximately ten more weeks of editorial work. Once in New York, Rizzo and Guitteau configured a video projection/5.1 monitoring environment - based around a Pro ToolsHD rig and a Mackie Control GUI interface - in Moore's own office. "Michael knew that he wanted something special and different for this film, something that he had never gotten for any of his other films," illustrates Rizzo. "He wanted to dedicate as many resources as he could for us, so he moved out of his office to allow us to use his room as a 5.1 sound studio for building the soundtrack."
With the film's picture editing department a halls-length away from the two-man sound crew, picture changes ebbed and flowed at a rapid pace. "As they would make changes, we would get them and immediately start work on them," tells Rizzo. "Now that sounds really great - like, 'wow, what a perfect, creative environment to be in' - but as great as it was, it was equally challenging. Picture changes are coming in rapid-fire. Because of the arrangement, they felt as if rapid-fire picture changes could be made and that we were going to keep up. That was really hard."
The unique work flow of the film didn't stop with the sound editorial's close proximity to picture editing either. "The film was broken down in a unique way," recalls Rizzo. "It wasn't separated into reels as a typical film would be but into conceptual segments. If you've seen the film, you know that it starts with Michael's, 'Was it all just a dream?' segment, leading into the theory of how the election was stolen and so on. Each one of those parts were broken down into a segment. From our perspective, the breakdown was difficult to manage because there were so many different sections that were changing so often. Luckily, the crew was small enough where - from a track management view - it was relatively easy to keep everyone informed."
For Rizzo and Guitteau, working only seconds away from all of Fahrenheit 9/11's source media and its chief caretaker - Archival Producer Carl Deal - was especially helpful when the duo was faced with troublesome audio. "Carl is one of the most amazing people I've ever met," praises Rizzo. "He was not only responsible for the licensing for use of all the footage in the film and getting the source material, he made sure that we had everything we needed. If we had a real 'dog' piece of audio we would turn to Carl. He would do additional research to see if there was something better somewhere out in the world. He was a huge help, and many times he really pulled the rabbit out of the hat."
EdiTrace To The Rescue
For picture cutting, the picture editors on Fahrenheit 9/11 used an Avid media composer, which is a video-based - rather than a film-based system. Because there aren't many video re-conforming solutions for video-based picture work, Rizzo chose to use EdiTrace, a program that provides a detailed list of changes between picture cuts in an edit decision list - or EDL - format. "We found EdiTrace after doing a lot of research on our options," Rizzo says. "EdiTrace will create a change note and will do the first auto-conform of a Pro Tools session to get it into a current picture sync. And for this film, it was key."
A secret service officer confronts Michael Moore across the street from the Saudi embassy in D.C.
Numerous selections of archival footage from many sources required varying amounts of restoration, whether it was using basic equalisation, complex filtering, or advanced noise reduction programs. "Through plug-ins and Pro Tools, we made sure that everything was automated," explains Rizzo. "When EdiTrace did the auto-conform, the plug-in automation was conformed with it. It was imperative that we have an auto-conforming solution to allow us to keep up with the picture department yet maintain all of the decisions for Pro Tools plug-ins. We were making thousands of those decisions daily, and all of them had to stay in sync with the current picture."
Reality Rules As much as Rizzo, Guitteau and Moore were concerned with the audio quality within Fahrenheit 9/11, maintaining a clear sense of sonic reality was of the utmost importance. "That's something that really needs to be stated," says Rizzo firmly. "Michael wanted to make sure that every detail presented in this film - whether it be visual or sonic - was truthful. He had no intentions of stretching things to any degree. If anybody had the ability to step forward and say, 'Ha! That's a sound effect,' you're busted. For instance, during the Iraqi War sequence, we wanted to make the bomb sounds big and real, but our number one rule was, Don't Doctor It Up. For creative input, we brought in some of the cameramen that were there shooting the footage we were using and other people that were there in Iraq during March 2003 when the bombings began."
During the film's highly emotional September 11 sequence, the screen is completely black for 90 seconds and the audience's attention is solely turned to sounds of the tragic day. According to Rizzo, this gutsy filmmaking move was a testament to Moore's confidence in audio's ability to effectively convey such a poignant moment in time. "It's a risky move," he explains. "You're providing no visual information for the audience to guide them to where you're trying to take them emotionally. But I think that it's a great indication of the respect Michael gives to sound as a medium."
For the sequence, every sound was captured on the day of the attacks within a few blocks of the World Trade Center. Rizzo: "Michael told us, that he wanted to make this a dedication and a tribute to the people that were there and on the streets within five or six blocks of the World Trade Center when the terrorist attack happened. He wanted to present the scene in a truthful way, and in a way that people haven't experienced it to better simulate what it was like to be there on that day. We did a restoration pass for every piece of audio that's there, a sound editorial pass to find out how each piece fell in line with everything else, and a mix pass within the 5.1 environment. With every sound, we intently questioned all sonic and emotional integrity."
'The Best Audio' Is Relative
While work for Fahrenheit 9/11 continued on to the final mix stage, Moore was still recording many of his final voice-over passes. Rizzo had brought in his recording rig to get the best tracks possible, but - following Moore's proven philosophy throughout the production of the film - the 'best' audio for the film wasn't always the most pristine.
"Michael cares a lot," says Rizzo succinctly. "He knew that the quality of this film needed to be something beyond anything he had ever done. That being said, as we were re-recording VO lines with my Schoeps mic and Grace pre-amp digitally feeding Pro Tools to get the most pristine recording, sometimes he still preferred the read of what he had originally done. His scratch VO tracks were recorded in the Avid cutting room; the window was open, you could hear New York City traffic and Avid fans spinning in the background. Still, he often felt that the emotional content of his original read - when he was assembling the picture and seeing it for the first time - offered the best performance and inflection. And to him, that was ultimately more important than the pristine recording."

PA Sistem Basic's


It may not be obvious, but a P.A. system is a precision instrument. Similar to the way that various components contribute to the makeup of a fine musical instrument, each element of a P.A. is critical to the operation and sound of the system as a whole. When the subsystems have been properly designed and implemented, the machine functions smoothly and effortlessly, accurately interpreting the commands of the user. Fine-tuning a P.A., avoiding phase problems while increasing clarity, efficiency and dynamic range, can mean the difference between adequate and great sound. A tweak here and there to a graphic EQ can smooth out harshness in the mids or reduce boom in the bottom, helping reduce listening fatigue. This month, Mix takes a look at some of the basic and not-so-basic things you can do to get the most out of a P.A.
BEFORE YOU TURN IT ONPlacement of speakers within a venue is critical to the quality of sound reproduction. Most important is avoiding feedback from the stage. The house array should be at least five feet forward of the front line of stage mics. If the P.A. is hung (or stacked) too close to the front edge of the stage, then feedback is inevitable. Line arrays may let you shave this distance by a foot or so, thanks to their directional control, but placing conventional boxes close to the performers is a recipe for disaster. In club situations, you may be able to get the house crew to push the house stacks forward (i.e., toward the mix position) to help avoid this problem. If that's not practical, or if the P.A. is flown, then pull the stage monitors and vocal mics upstage a bit to get them farther behind the house stacks.
Loudspeaker cabinets should not be flown or stacked within the arch of a proscenium because the proscenium itself can cause reflections that will interfere with the cabinets' intended dispersion pattern. In Atlantic City, N.J., the House of Blues actually added hang points in front of the proscenium to get its array farther into the room and out of the sonic influence of the proscenium.

Venues with large stages (wider than about 50 feet) present a problem for audience members in the first few rows. People in these seats won't hear vocals from the P.A. because they're too close to the stage and the P.A. is throwing sound to areas behind them. Sometimes the monitors spill vocals into the audience, but this may not be enough, and if the entire band is using personal monitors, then there will be no spill of any sort from monitors into the audience. In these situations, a front-fill is necessary.
The fill can be a compact speaker (EAW JFX200, L-Acoustics 112P, Electro-Voice X-Array Xcn or similar) with a 12-inch woofer and a 2-inch horn. Three such cabinets distributed across the front edge of the stage will usually do the trick. Amplification for these speakers can be fed from a matrix that carries only the vocal channels (and perhaps piano or some lead guitar), as the remainder of instruments usually can be heard from the stage. You'll need to listen from the front rows during soundcheck to determine how loud the fills need to be; bring them up just loud enough to add presence to the vocals — but not loud enough to disturb the main house mix.
Time permitting, every driver in the entire P.A. system should be checked for proper polarity. Obviously, this is more easily facilitated when you're the systems engineer and performing an install, but it's possible to do this even if you're a guest engineer. A polarity checker (more commonly and incorrectly referred to as a “phase checker”) can help, provided you observe two important guidelines: The device must be within inches of the driver and you must be able to perform the check with only one driver operating at a time. If you cannot use a polarity checker under these two constraints, then don't bother.
An oft-ignored aspect of loudspeaker placement (especially at the club level) is the relative position of high/mid/low-frequency drivers in P.A.s employing separate cabinets for these drivers. All drivers should be time-aligned for phase coherence. Time-alignment is physically achieved when the acoustic centers of the drivers are equidistant from the listener. An alignment error may not be apparent to the casual observer, particularly if the high/mid cabs are flown and the low or sub cabinets are ground-stacked.
In club situations, the subs are often downstage of flown mid/high cabs, meaning that arrival time of sound emanating from the high/mid cabinets is different from the arrival time of sound emanating from the low or sub cabinets. This results in phase errors, which are most apparent at frequencies near the crossover point(s). If you cannot physically arrange the boxes for proper alignment, then do so electronically. Just about every loudspeaker processor manufactured these days incorporates a separate delay for each output, so set a small delay to compensate for the difference. The rule of thumb is 1 ms of delay per foot; delays in this context are typically 1 to 3 ms.
While you're at it, delay the house stacks to the instrument backline by measuring the distance between the backline and the P.A. Delay the main system by roughly 1 ms per foot. In small clubs, this can make a marked improvement in low-frequency clarity because the P.A. can be brought in-phase with the backline. While it certainly won't hurt to initiate this delay in an arena situation, the ratio of P.A. to stage sound is much higher than in a club, yielding less-dramatic results.
If the opportunity presents itself, don't be afraid to vary the mix position. In spite of the fact that many engineers prefer to be centered between the left and right stacks, this listening position may not be representative of what the majority of the audience hears. P.A.s tend to “focus” in the center of the room, so when you're mixing at center, you'll hear more low end than those folks seated on the sides will. Conversely, setting the mix position closer to one side yields less low end than people in the center seats will hear. Either way, you'll need to make a mental “mix adjustment” to the low-frequency content of your kick drum and bass feed so it's consistent for as much of the room as possible.
MAKE SURE IT WORKS!Having addressed some of the physical aspects of loudspeaker placement, turn on the P.A. and focus your attention on ensuring that all drivers and amps are operating properly.
Run pink noise through the system and analyze the result with a real-time analyzer. RTAs are no longer the domain of the rich and famous. Handheld models that include SPL metering and noise-generator functions can be had for as low as $300 and are worth every cent, especially when you mix on different systems every day. If you prefer using a computer for audio analysis, check out SIA SmaartLive or Metric Halo's SpectraFoo Complete, both of which include powerful audio diagnostic tools. (One of my favorite diagnostics is SpectraFoo's Transfer function. It can tell you what happens to frequency response and phase of a signal as it is passed from the input of a mixing console through to the output of a drive processor.)
Regardless of what measurement tool you are using, run noise from the generator into a channel with EQ set flat (and no processing) and route it to only the left side. Set the left and right master faders for the same gain and measure the SPL using a slow response time. Pan the signal to the opposite side and again measure the SPL. A difference of more than a dB or two indicates something is wrong. Possibilities include a power amplifier not being turned up all the way, a damaged speaker component or mismatched crossover settings. (More about that later.)
With the signal panned to one side, set the RTA to a slow response and observe the RTA curve. (Your meter or software may let you store the measurement.) Then pan to the opposite side. The RTA should show the same results within a dB or two. If not, use a ⅓-octave EQ to match the frequency responses of the left and right channels of the P.A. If the two don't sound the same, you'll go crazy trying to mix. Most P.A. systems also incorporate a compressor on the left/right bus, so pay attention to the position of the compressor in the signal flow; EQ'ing before the compressor can trigger compression.
Another suggestion for a quick checkup? Turn all faders down and patch a click (from a metronome or a test CD) into a channel on the console. Set the EQ flat, route the click to the left bus, slowly turn up the faders and listen. With the volume still way down, walk up close to the P.A. and listen to each cabinet to make sure it is producing sound. (Have someone baby-sit the console so that no one accidentally turns up the gain.) Repeat for the right side of the P.A.
If the P.A. system incorporates a loudspeaker processor (such as a BSS Omnidrive, dbx DriveRack, etc.), then mute all outputs on both channels. One at a time, turn on each output and listen to the system's sub, low, low-mid, mid- and high ranges, making sure that each range is working for left, right and (where applicable) center channels. If the system does not have a processor, then use a channel EQ to filter out the lows and mids, emphasize the highs and check the HF drivers. Then adjust the EQ to filter out the high and low range and emphasize the mids, etc., each time listening to the output of a particular range to make sure it is operating.
Be aware that playing music CDs through the system may not reveal problems with tired, borderline drivers, particularly in the low end (more on this below), so use a reference-test CD or tone generator to play sine wave tones ranging from 50 to 16k Hz through the system. (Don't use square waves as they mask distortion.) Low-frequency tone will quickly reveal woofers with voice coils that are rubbing, as well as rattling grillework or metal-to-metal contact near speakers. Third-octave tones can help reveal P.A. “hot spots,” which often show up at resonant horn frequencies of 1.6 kHz, 3.15 kHz and 6.3 kHz, and can be easily tamed using a 31-band, ⅓-octave EQ.
If a particular frequency range is especially hot, turn your attention toward the output controls on the loudspeaker processor to turn down (for example) the drive to the mid- or high-frequency amplifiers. (Do this before going for the EQ.) You may also need to tweak a crossover frequency (or slope) if there is too much energy due to overlap between the mids, high-mids and highs. A slow sweep tone played through the system should sound smooth and consistent through each range, with no hot spots.
INVESTING IN CDSMany engineers use a favorite CD to tune P.A. systems. They become very familiar with a certain piece of music and they know how it should sound over a variety of different sources, such as headphones or studio monitors. Try listening to the piece of music through the P.A. and applying EQ until it “sounds right.” There's nothing wrong with this approach, but keep in mind that a CD — with its processing, compression and mastering — is not representative of the transients encountered with amplified live musicians. An alternative method employs using a vocal microphone for equalizing a system. (Carry your own mic for consistency and hygiene.) Talk into the mic to excite the resonant frequencies of the P.A. and then use EQ to correct them. In this case, you're using the same tools that you use in your live mix: compressors, equalizers and mics (as opposed to a CD).
Another technique calls for plugging a CD player into two channels of the desk and bypassing the channel EQ and the system graphic EQ. At the power amps (not the crossover), turn down the subs and the tweeters and listen to the midrange only. Slowly add the subs and tweeters into the midrange until you think it sounds balanced. If it's still necessary, use a graphic EQ for correction, but keep in mind that many engineers feel that any graphic EQ distorts the phase relationship of the input signal.
MIND YOUR BOTTOMThe majority of sound systems are set up with the L/R bus feeding signal to a drive rack (or crossover), which in turn divides the audio signal into various bands and routes signal to various amps in a multi-way P.A. In this type of system, it is possible to send a signal to the subwoofers that has no business being there, such as a hi-hat or lead vocal mic. Hopefully, the engineer has the smarts to use a highpass filter to remove whatever low-frequency crud might make its way into a hi-hat mic in the first place — thus preventing that signal from ever reaching the subwoofer.
However, if you really want to mind your bottom, here's an alternative approach: Use one of the console's auxiliary outputs as a subwoofer send. This concept removes unwanted audio from the subwoofer simply by virtue of the fact that you turn up the subwoofer aux only on the channels that need to be in the sub. Channels such as kick drum, floor tom, bass guitar and synth get fed to the sub aux, while channels such as lead vocals, hi-hat and the triangle microphone do not. The aux output designated as the subwoofer feed is usually routed to a crossover or lowpass filter, from the filter to a compressor and then to the subwoofer amplifiers.
In lieu of a “proper” crossover, I've seen engineers run the sub aux out from the console to a single-channel, 31-band EQ with all of the high-frequency sliders (say, those 125 Hz and above) pulled down all the way — thus acting as a filter for the high frequencies. Make sure that this aux is set to post-fader, or your low end will become disproportionate every time you move a fader. But be aware that when you mute the main L/R outputs of the system, the sub aux will not be muted and your audience will hear low-frequency rumblings from the subs.
While we're on the topic of low end, don't forget to take advantage of the highpass filters provided on each input channel. During soundcheck, audition each input over the P.A. (not headphones) one at a time, turn on the highpass filter and bring up the cut-off frequency until you can hear the low end start to drop out. Then back it off a bit. This will keep unwanted sounds such as mic stand rumble from ever reaching your low-frequency amps, preserving clarity in the bottom end and maintaining system headroom.
Tuning a P.A. system doesn't have to be rocket science, and the payoff is well worth the effort. The most important tools you need — your ears — are free. With planning and diligence, you can make the most of a subpar system or bring a state-of-the-art system to its highest level of performance.