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Sound Advice

Everything Is An Amplifier Part III by Bryan Martin

October 19th, 2007

Every amplifier has a sound. Mankind is still searching for the audio grail of a “straight wire with gain.” What a great amplifier does is transfer the maximum amount of the information from its input to its output with as little damage as possible. This translates into full bandwidth, wide dynamics, and undamaged transients: the essentials of great sounding reproduction.

In the brave new world of the 21st century, technology has brought incredibly powerful tools to the everyday. Recording studios live in a laptop, and declining are the great temples of sound recording and the monks who populate them. We take music for granted. We take technology for granted. We want it all in a bundle. And very few people have the privilege of experiencing music in an ideal listening environment. Ear-buds, iTunes, and laptop speakers are a pale copy of a breathtaking audio system. As the audio chain gets dumbed down, there is all the more reason to give recorded sound the best possible vehicle on its way to immortality. Because after it is committed to a stream of digits, the road it takes back to sound will be challenging.

Equalization, compression, and the like are often reached for in an attempt to correct a sound source that is lacking. I have always been baffled by manufacturers who package a mic preamp, EQ, and compressor all in on package. If the mic preamp was good in the first place, then why the need for the compressor and EQ to fix the sound coming out of it? Note: Manufacturers spout specs and tech-speak, which may well sound impressive, but to the educated reader is often contradictory or plain rubbish.

Audio specs are like accounting: you can make them look like whatever you want. But specs don’t translate into good sound. There are plenty of horrible-sounding units out there with amazing specs. To cheaply achieve good bandwidth, hideous mechanisms are employed in the signal path. Using a large amount of negative feedback will drive the bandwidth into the nether regions of the sub and supersonics, and also completely kill the sound quality. People listen with their eyes these days, not their ears. How often do we find ourselves staring at the waveform while it plays back out of a workstation. It has become a reflex almost totally associated with the listening experience. The box looks great; it has to sound great. But that is not always the case.

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.

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

August 19th, 2007

A Star grounding scheme, in which all equipment in an installation is bonded to a central ground hub, can be useful for minimizing low frequency common mode voltages between various pieces of equipment if it’s properly implemented. If not properly implemented, star grounding can result in performance, which in some cases is actually worse than that resulting from a completely haphazard approach.

Any secondary grounding system installed in parallel with already existing equipment U-Ground conductors in an installation has the instant effect of causing far more potential ground loops between equipment than would otherwise exist. Sometimes it makes a difference, sometimes it doesn’t. The $64 question is whether it reliably, and without exception, makes noise go away permanently and completely. Not likely.

A popular Star Grounding practice involves using separate ground wires to bond all equipment in the ensemble to a central hub, and then connecting this hub to a dedicated earth-grounding terminal, which is not bonded to the main building ground system. This practice is very dangerous and is completely illegal in the context of North American Electrical Codes.

One connection between an ensemble of equipment and building ground is all that is needed to make the system safe in terms of both the letter and intent of applicable electrical codes. Most installations usually involve more than one AC power circuit, whether actually required due to the size of the total load or not.

What is not considered in such a scenario is how long and by what path(s) the power circuits and their respective equipment ground conductors take before they get back together at the breaker panel. Just because two outlets are within a few feet of each other does not necessarily mean that they are on the same circuit.

In smallish installations in which all equipment is in one area/room and the longest audio cables are perhaps less than 100′ in length, and assuming that the breaker panel is somewhere else in the building, a very effective approach is to arrange to have all of the power circuits end up at a point in one box in the middle of the equipment ensemble. Very often, this middle point would be in the floor trench under the tabletop of the producer’s table equipment cabinet behind where the engineer/producer sits.

Install as many circuits as you think you need. What this scheme buys you is that by bringing all circuits into one multi-gang outlet box, all of the associated equipment ground conductors (one per circuit) also end up in the same box, all bonded together as prescribed by code. This star point becomes your one connection back to building ground, with the added advantage that now you have a demonstrably lower impedance path back to building ground by virtue of having X paralleled equipment ground conductors.

From this central box, 3-wire branch circuits are then run out to each grouping of equipment. If at all possible, all of these circuits should be in one continuous raceway/conduit, so that the associated equipment ground conductors are daisy-chained throughout the facility. This ensures that the total length of the equipment ground conductors between different equipment locations within the room is as short as possible. For only a few circuits, series-connected power bars are acceptable for this application, but use good ones and try to stay away from conventional “Surge Protected” ones, which employ Metal Oxide Varistors (MOVs) – they have been known to start fires when they ultimately outlive their service life. This ensures that the total length of the equipment ground conductors between different equipment locations within the room is as short as possible. As simple as this seems, this approach may eliminate enough residual noise so as to end the effort to go any further.

“OK wise guy, so what happens when I then run shielded audio cables all over the place?” you ask. “Don’t I end up with a big bunch of ground loops anyway?” Yes you do. Minimize the areas of the resulting ground loops by selectively cutting cable shields at one end or the other, the One-End-Only (OEO) approach. This is a simple way of smothering the symptoms of Pin-1 problems, and while in larger systems it may be required for other reasons, it’s usually not necessary in a small installation – besides which, it’s a pain in the ass and you can’t do it anyway in unbalanced single-conductor shielded cable installations for reasons which should be obvious. What you can do to minimize these loop areas is to simply run all of the low-level audio cables parallel and adjacent to your new branch power cables.

Be sure to pick up the October issue of PS where Muncy delves into the Pin-1 problem and other RFI solutions.

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.

Everything Is An Amplifier Part II by Bryan Martin

August 19th, 2007

Once all of the requirements of a gain stage are met [as outlined in the June issue], the designer will then select the ideal requirements for a specific stage, but achieving these requirements rarely happens in the real world. Attaining one design goal is often at the expense of another. There will be limitations imposed by the characteristics of the gain device chosen, economics, physics, and a host of other factors. And as the number of stages increase, so does the difficulty in bringing them all into an optimum specification.

Great sounding amplifiers require high-quality components. Transformers used in power supplies and for audio I/O are both large and expensive. Quality coupling capacitors, gain devices, and hardware all drive up equipment costs. The classic and highly sought after Neve modules have large, expensive power supplies, plenty of transformers, and build quality of impeccable craftsmanship. You will also notice that these Neve consoles have a far simpler layout and less options than the later generation Neve V Series, SSLs, and the like. Generally, a very well-implemented, simple gain path will always out perform a complex one – and negates the need for further processing.

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.

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.

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