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Sound Advice

Star Grounds, Loop Areas, & Electrical Safety In Project Studios, Edit Suits, & Other Compact Audio Installations Part by Neil A. Muncy

June 19th, 2007

Earth “ground” connections were first implemented well over 100 years ago as a defense against lightning entering buildings on early power lines, and to minimize peak voltage in industrial electrical equipment, which were often located many miles from generating plants. Improving electrical “people safety” was the name of the game back then, and things haven’t changed since.

Nineteenth century electrical engineers used the word “ground” to describe a deliberate connection to the earth to minimize the risk of damage from lightning and power surges entering a building on the power lines. In North America the concept of earth ground connections has been refined for the principal purpose of making electrical equipment as safe as possible for the masses.

Ground has taken on a vast number of often confusing, contradictory, and/or misleading meanings, especially in the audio world. For the purposes of this discussion, lets just use Ott’s definition #2 [1]: “A ground is a low-impedance path for current to return to the source.”

Note: In North America, the means and procedures required to ensure adequate electrical safety in buildings are specified in the US National Electric Code (NEC) and the Canadian Electrical (CE) Code. These specifications are legally enforceable.

“Ground wire” is a contradiction in terms. The word wire is just another term for describing an antenna. Mother Nature does not read labels. You say, “… 5′ cable,” Mother Nature says, “… ½ wavelength antenna in the middle of the FM broadcast band.”

All conductors have inductance directly proportional to their length. Wind a conductor into a coil, and/or make it longer, and you get more inductance. Inductors oppose the flow of AC current. Increase the frequency, and there is more opposition to current flow.
Therefore, realize that a long ground wire from point A to point B is only really a useful ground conductor at very low frequencies, but there are a lot of folks who never considered, and/or believed, and/or understood this basic fact of physics. When electrical equipment is bonded together with ground wires, and there is more than one conductive path between any two pieces of equipment, a ground loop is formed.

Be sure to pick up the August issue of PS for an in-depth look at star grounding and loops.

References:
[1] OTT, Henry W., Noise Reduction Techniques in Electronic Systems, (2nd Ed., John Wiley & Sons, 1988) ISBN 0-471-85068-3

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by e-mail at: nmuncy@allstream.net.

Tips On Getting Killer Drum Sounds by Nick Blagona

June 19th, 2007

Engineers spend more time getting drum sounds than any other instrument. I’ve personally seen situations where days have been spent getting a drum sound. Kits are changed, heads are changed, cymbals are changed, heads are taped up or un-taped, mics are selected and changed, the kit is placed in various parts of the studio, head damping devices are used, mini pads are cut up and placed on heads, and on it goes. The poor drummer keeps hitting his kick, snare, and toms … by the end of this, he or she is back in rehab.

Here’s my approach for a great drum sound. My recommendations for drum mics: Sennheiser MD 421s, Shure 57, and some Neumann 87s. I like using the Neve 1081 console in Studio 1 at Metalworks, so all frequencies mentioned here are from the 1081s. I find that padding down the preamp a low as you can go with the fader up gives me the best result. Having the mic pres all the way down gives me very little leakage from the cymbals to the toms and hi-hat to the snare and very little kit in the kick drum.

The Kick
Mic the kick drum with a Sennheiser 421, throwing a sandbag in the drum helps to dampen out any overtones. The mic should be placed right at the beater. I also use a Yamaha NS10 woofer as my second mic, placed where the front skin used to be. I record this flat since it has the prefect frequency response.
For the 421, give it +3 at 82 Hz for bottom and +4 at 6.8 K for added attack.

The Snare
For the snare drum, use the Shure SM57 at a 45- to 60-degree angle about an inch or two above the head pointing it at the centre of the snare.
+2 at 82 Hz, -2 to -4 at 820 Hz, and +4 at 6.8 K for crispness. If you like the idea of miking under the snare for some rattle and hum, use an AKG 414 in a tight pattern under the stands.

Toms
Mic all three toms with the 421s set at about a 45-degree angle to the centre of the tom. I usually add
some 8.2 K.

Overheads
For the overheads use U 87s. Place the mics about 16″ over the cymbals’ centres and towed out at about 45 degrees. I usually record them flat.

Hi-Hat
An AKG 451, pointing at the centre.

Nick Blagona has recorded The Bee Gees, Chicago, The Police, The Tea Party, Alexisonfire, Deep Purple, and many others. Please go to www.nickblagona.com for more details.

Everything Is An Amplifier Part I by Bryan Martin

June 19th, 2007

The basic building block in audio is the amplifier. When the word is mentioned most of us have the image of a power amp pop into our heads. They get all the press because they are the largest and most glamorous of the species, but what about the myriad of smaller and forgotten gain stages that occurred before the signal arrives at this last power stage? They are largely anonymous and taken for granted, but determine the quality of recorded sound.

Almost every knob on a piece of audio equipment is controlling a specific amplifier stage. And the farther we get away from the basic understanding of this simple entity, the farther we get away from knowing how to maximize its sonic potential.

The steady advancement of technology has served to obscure their very existence. Amplifiers have become so small and commonplace that they have virtually disappeared from human consciousness. Just look at the iPod nano – that thing is loaded with amplifiers, all crammed onto a little chip and powered by another sliver of technology.

The implementation of each gain stage, individually, and then as a complete amplifier, determines the sound quality of a piece of audio equipment. This fact seems to have been largely lost in the mysteries of time. Most people don’t even realize the devices they use even contain an amplifier. It just works.

In recent years, there has been an onslaught of multi-function units, recording channels, and the like. With the recording business moving from a professional to a consumer market, manufacturers are trying to offer the most features for the price. This looks great on the outside, but there is a large cost on the inside. The quantity of functions within a unit is usually inversely related to its sound quality. Fundamentally, it is difficult to design a good-sounding, multi-function unit, because every gain stage comes with the constraints of its implementation.

The requirements of a gain stage are:
1. Its gain coefficient. (With a coefficient of 10, 1 V input will give 10 V output.)
2. Bandwidth. For audio we generally want to double the range of human hearing (20 Hz to 20 kHz) so that would be 40 kHz to insure good transient response.
3. Input impedance.
4. Output impedance. (Generally we want to have the output impedance of the previous stage low in relation to the stage that it is driving to minimize the losses in the coupling between the two stages.)
5. Maximum output signal before clipping.
6. Maximum input signal before clipping
Pick up the August issue of PS for Part II.

Bryan Martin owns Sonosphere Mastering. Over his 20+ year career he has worked with David Byrne, Rufus Wainwright, Max Roach, Run DMC, and White Zombie. He can be contacted via e-mail at bryan@sonosphere.ca or on the web at www.sonosphere.ca.

Roger’s Rules of Compression by Roger Nichols

April 19th, 2007

1: Don’t. I would rather spend the time to ride the solo or vocal to get a cleaner sound with no compression artifacts. I also prefer to manually remove pops and sibilance. You can use the volume automation in a DAW to eliminate vocal pops and sibilance problems by drawing a V-shaped notch at the center of the pop or ess. It does not have to be very wide, and it will work better than any automated de-esser or pop filter.

2: For the most transparent compression, use a ratio between 2:1 and 3:1. This will increase the apparent loudness of your vocal, but will not have that annoying pumping sound of badly adjusted compressor settings.

3: Don’t compress more than 4dB. Watch the gain reduction meter on the compressor. Adjust the input gain or threshold level until the reduction reads between 3 and 4dB, no more.

4: Use multiple compressors connected in a series if you need more than 4dB of compression. Set the attack and release settings differently and you will have more compression without sounding like you’re killing the vocalist.

5: Parallel compression works in some circumstances. You have the dry signal and the compressed signal – mix them together to get the sound you want. Make sure you compensate for any delay in the compressor to avoid phasing.

Roger Nichols is a recoding engineer and producer and has won seven Grammy Awards, the 2001 TEC Award, and received 11 Grammy nominations. He is on the Board of Governors for the Miami Chapter of NARAS and lectures at Berklee School of Music, Musicians Institute, Recording Workshop, Full Sail, Vancouver Film School, and University of Miami. Visit www.rogernichols.com.

5 Tips For Stalking, Managing, & Capturing Rogue Sounds With Traps & Baffles by Russ Berger

April 19th, 2007

Employing Sound Traps and Baffles is much like hunting.

1. Know your hunting grounds: Before the hunt, know and understand your acoustical environment. Once you bound a space with walls, a floor, and a ceiling, you’ve committed acoustics. The boundaries of your space define the low frequency modal response and set limitations for the ambient decay time. Wonderful programs and countless texts have been written that clearly describe the process for analyzing, predicting, and managing acoustical boundary conditions.

Once you understand your environment you will better know how rogue sounds behave in the space; you can better identify where problems might lie and devise a trap to capture the problem.

2. Put the traps where the beavers are: Place traps to capture rogue sound much like you’d place traps for beavers. Placing beaver traps on the ceiling will do you little good, just like placing acoustical traps where the sound you want to capture doesn’t exist. Beavers pretty much live their lives along the floor plane. But rogue sounds live in the three dimensional world, so successful hunting can be achieved if the traps are placed in proximity to boundaries and intersections.

3. Be sure your passive trap is big enough to capture your game. Lower frequencies require larger and deeper traps to control and manage long wavelength rogue sounds.

4. Know how many you want to trap: Trapping one beaver vs. an entire colony will require different methods. The effective trap absorption efficiency is proportional to the area of coverage.

5. Conceal the trap: A good looking studio always seems to sound a little better. Integrate your traps into the architecture and along with those rogue sounds you’ll catch new clients.

Bonus Tip #6: go to www.RBDG.com – Russ Berger is Owner of Russ Berger Design Group (RBDG), which is a design and consulting firm that combines expertise in acoustics, architecture, and interiors to create technical environments and buildings for recording studios, broadcast facilities, creative production spaces, and home theaters.

Grounding, Shielding, Hums, Buzzes, & Things That Go Zap! In Your Sound System by Neil A. Muncy

April 19th, 2007

Noise susceptibility (or the lack thereof) in audio systems is a function of two principal factors: shielding, and the “pin-1 problem.” The endless conversations concerning this matter inevitably involve earth “grounding,” a subject which has been around for so long (200+ years) that it has devolved into a sea of confusion, misinformation, and mythology, even though it is completely dictated by easily understandable basic physics.

Conventional grounding mythology would have one believe that electronic systems of all kinds must be robustly connected to earth ground in order to properly function – audio signal processing systems in particular. The grounding reality is that airplanes, motor vehicles, laptop computers, blasters, etc. seem to work just fine without connections to earth ground. Nevertheless, A/V systems of all kinds are considered exempt.

According to the conventional mythologists, “noise in audio systems must have something to do with grounding, what else could it be?” The bad news is that the short answer to this question would fill up this entire issue many times over. The good news is that on the Professional Sound website www.professional-sound.com, a long list of reference material will be found. In addition, the June 1995 issue of the Journal of the Audio Engineering Society, entitled “Shields and Grounds,” includes seven papers which directly address this matter. Go to www.aes.org, and look up “Special Publications.” It’s available as freeware to anyone for $15 US, less if you’re an AES Member … it may also be downloadable. It won’t take you long to realize that the conventional mythologitsts just might be wrong!

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by email at: nmuncy@allstream.net.

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