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Good Amps and Power Efficiency

Wednesday, December 18th, 2002

PA amplifiers need to combine the delicacy of a good hi-fi amp with the robustness and reliability of a farm tractor, blending (increasingly) with the low weight and compactness of aeronautical gear.

Good-sounding power amps (ones which add minimal colouration or distortion to the signal, purely making it louder) require great sophistication to enlarge and deliver the signal very precisely over a wide ‘canvas’ of levels and frequencies, while also delivering high currents and voltages.

And these quantities are not delivered into docile power-absorbing elements, but instead into speakers, which are quite complex and ‘reactive’ in the way they interact with the amplifier.

No power amplifiers are 100 per cent efficient – even the best manage only about 80 per cent in reality. The best speakers, meanwhile, only approach 25 per cent efficiency. Best overall efficiency is consequently about (0.8 x 0.25) = 20 per cent.

The average overall efficiency figure is more often between five and ten per cent. Taking ten per cent as an approximate figure, this means to get a certain amount of acoustic power – in other words music at a suitable sound level – in the room, we have to provide about 10 times that power from the electricity supply. And so this is the amount that an audio power amplifier has to handle and ‘process’.

We’ll also want to have some power capability in reserve – since inadequate power results in amplifier overload and bad sound. In general, erring on the side of over-rating is better than under-rating.

And remember that the relationship between watts and loudness isn’t proportional in the way you might imagine. As a reminder, a rule of thumb is that you need to increase the power delivery into any particular speakers by at least tenfold (x10) to attain about twice (x2) the audible level. This appears on a sound level meter as a 10dB higher SPL (sound pressure level) – so, for example, if 100 W gives 90dB SPL, 1,000 W will be required to increase the level (where nothing else is altered) up to 100dB SPL.

In short, much, much more power is needed than you might expect.

This article is reprinted with permission from The Live Sound Manual, published by Backbeat Books, www.backbeatbooks.com. All information is copyrighted and cannot be reprinted without the permission of the publisher.

Recording The Lead Vocal

Wednesday, December 18th, 2002

How Many Tracks Is Too Many?

More often than not, the lead vocal is the track that contains the most emotional content of the song. With repeated attempts at recording the vocal, you run the risk of losing that emotion and “magic”. So while it’s ideal for the singer to nail the perfect take in one or two tries, a good engineer knows how to respond the other 90 per cent of the time.

The answer is to compile the best elements of a few different takes into a single, composite performance where each line, each phrase and even each syllable is sung just the way you want. This process is called “comping”. It’s done on nearly every record you hear, even the ones you’re convinced are single, complete takes.

Tip: If the singer is hesitant to record this way, claiming “artistic integrity”, remind them that they’re free to sing the song through from top to bottom, without interruption. Meanwhile, just switch tracks while you’re winding back to the top after each take. (Make sure you’re only sending the current take to the headphone mix – it can be very disconcerting for a singer to begin a song and hear two voices coming out of his mouth.)

In this digital age of virtually unlimited available tracks, it’s tempting to record 5 or even 10 different takes before comping the vocal. But using that many can really overwhelm you and confuse the process. Try utilizing two or three tracks instead. Starting with your first take, tell the singer it’s only a practice take for the purpose of further level adjustment (when in fact you’ve already adjusted everything and are ready to go). This is useful for anxious singers, taking the “pressure” off them.

After two or three takes, stop if you have terrific performances overall. If not, go back to the track with the least inspired take and record over it. Hopefully, you have gained the singer’s trust by now and don’t need to inform them of these details. Continue with this process until you feel that, within those two or three tracks, you have the makings of a great performance.

When you’re ready to start comping, draw lines on the lyric sheet so you can make little notes (check marks, yes, no, good, bad, maybe) on each line of each take. Involve the singer in this process only if they insist – the more they analyze their own performance, the less they’re likely to respond with an inspired, heartfelt one. Once you have usable takes for each line, bounce the winners onto a fresh track (you can also bounce certain lines from “alternate” takes into one take that just needs a few fixes).

Tip: After you have a comped vocal, get away from it for a while (dinner break, TV break, whatever). Then listen to it with fresh ears, and with the singer, to see if you still need to fix something.

This article has been reprinted from the Studio Buddy software. Written by acclaimed producers/engineers Michael Laskow and Alex Reed, Studio Buddy gives hints and tricks on various recording techniques. To download a free copy, go to www.studiobuddy.com.

Crossovers: How Many ‘Ways’?

Wednesday, December 18th, 2002

Whether the crossover is set up for two, three, four or more bands will be largely pre-determined by the PA’s speaker system. Here’s an outline of what the different numbers of ‘ways’ generally accomplish, and how they’re placed.

Two-way crossover systems require a minimum of two amps, so they’re referred to as bi-amped. The split signal feeds just low frequency (LF) and high frequency (HF) drivers. Such a simple set-up is typically restricted to monitors or mini PAs, because for most kinds of music it’s not possible to cover the audio range fully enough (particularly with low-enough bass) with only two types of drive units.

Three-way systems (sometimes called ‘tri-amped’) feed low-, mid- and high-frequency drive units, and are the most widely used configuration for ordinary FOH PAs and more elaborate stage monitor cabs.

If you require a three-way PA system on a tight budget, you can use set-ups such as ‘bi-amped + passive split’ or ‘two-way active with passive split.’ All that’s required is a single two-way stereo crossover, a minimum of one stereo power amp per side and three-way cabs wired for this approach. The system is still bi-amped, but is also three-way. It’s achieved by ‘splitting’ the HF band’s signal (really mid + high) using an additional passive crossover in each mid/high speaker cab. Hence ‘passive split’. The active crossover splits the bass from everything else. The passive then splits the HF from the midrange – like a sequence of two forks in a road network.

Despite the limitations of passive crossovers, passive splitting of HF (only) can work quite well.

One restriction of the ‘passive split’ configuration is that the top-end’s level can’t be limited with any discrimination – any protective limiting is ‘lumped in’ with the midrange (we’ll cover limiting in more detail shortly). But this only affects the ultimate sound level capability. The excess levels in one or the other will turn down both. Still, the limit has to be set low enough to protect the tweeter, rather than the mid, which would handle more power.

If higher sound levels are really needed, more active ‘ways’ are simply going to be required. But you can still add a passive split to these.

Typically this is done for occasions when super-tweeters (working at frequencies above about 14-16 kHz) might be used – for example providing a PA in a small venue where high frequencies won’t be largely absorbed before they’ve reached the audience.

Four-way crossovers (quad-amped) will either send signals to a sub-bass driver, plus low, mid and high units; or else to low, low-mid, high-mid and high-frequency speakers. It’s mainly used for more up-market FOH PA.

Five-, Six- and Seven-way
These were more common in the past, when PA developers experimented with different schemes – and before accountants worked to prune tour costs to the bone. The frequency ranges became further sub-divided and the speakers used were increasingly specialized. These higher-way systems are more complex, but offer potentially higher sound quality and ‘maximized’ power handling.

But the ‘law of diminishing returns’ sets in fairly steeply once the crossover has split-up the audio range into four fairly equally-sized bands. For one thing, the weight of amps and cabling, as well as the wiring and rigging complexity, is bound to start increasing substantially, but without much worthwhile increase in sound level or quality. There’s also an acoustic trade-off, in that it can be increasingly hard to synchronize larger numbers of separate sound sources.

Despite this, you will occasionally still meet five-, six- and seven-way systems. There are commercial analog (active) crossovers with five and more bands, some of them flexible modular types. Or else they’re bespoke (custom-made), way crossovers. The more upmarket digital crossovers also typically offer up to six bands.

This article is reprinted with permission from The Live Sound Manual, published by Backbeat Books, www.backbeatbooks.com. All information is copyrighted and cannot be reprinted without the permission of the publisher.

Becoming a Producer

Wednesday, December 18th, 2002

Almost as soon as assistant sound engineers learn enough about studio recording to spell “EQ”, their ambitions begin to drift towards the possibility of working as a producer. They see dollars, or power, or the seductive pull of being totally in charge of the artistic direction of a recorded work, and sooner or later, I get the inevitable question: “How do I go about becoming a producer? Is there a course I can take?”

It all depends on how you define “producer”. In its simplest sense it can mean anyone involved in sound production – so if you are a songwriter, musician or sound engineer, you could be regarded as a “producer of sound…”

If that’s what you want (and you have the talent), then experience, skills in recording (i.e. “music production”) can be gained through on-the-job training, sound engineering courses or a combination of both. There are many courses from which to choose.

However the term “producer” in its more accepted sense describes the person responsible for the total sound and feel of the finished track. Responsibilities generally include choosing and arranging songs, selecting and rehearsing the band and any additional musos, working with the engineers during tracking and mixdown, and guiding the mastering engineer during final post-production.

The producer may employ others to help realize their vision, or may take a hands-on approach to some of the duties such as recording or mixdown. In any event, a producer generally leaves the imprint of their own style on the finished product while still allowing the style and talent of the performers to shine through.

Becoming a recognized producer therefore involves developing a professional skill-set through a number of different avenues. Essential areas include music knowledge, theoretical, technical and practical knowledge of sound engineering, mixing and post-production. A very good set of ears and ability to work effectively with people is a must. A knowledge of the capabilities of a wide variety of studios and other audio facilities helps too.

Audio courses may help, but they need to be extremely comprehensive. The Germans have a word for the technical side of a producer’s job: “Tonmeister” – Master of Sound. There are some “Tonmeister” courses around, but check first that they are respected by the industry, because there are some that are “Tonmeister” in name only. One of several courses with a good reputation is the degree course at Surrey University in the UK. Any short, part-time courses claiming to make you a “Master of Sound” may be stretching the truth just a little!

Whether you do a course or not, without a track record in the real world it is unlikely that you will ever get a producer’s gig – unless you are very persuasive.

Many successful producers have not completed any formal training at all, except perhaps for music. They have paid their dues through the experience of being musicians and engineers and show such a fine grasp of the sensibilities of putting together recorded works that others ask them for help with their music.

When that happens, and continues to happen, you are a producer.

Vyt is the Managing Director of Audio Training Consultants, who operate the audioEd Pro Audio Resources Site, www.audioed.com.au. Before ATC, Vyt owned and operated several professional recording studios and an accredited audio school for more years than he cares to remember.

In With The Old, Out With The New

Wednesday, December 18th, 2002

Three Reasons to Reconsider High Technology

Reason 1 – Analog audio had been refined to an art form with its origins dating back to Alexander Graham Bell. While tube technology was extremely inefficient due to heat loss, it sounded very pure and warm. Transistors were bulky compared to integrated circuits but they were produced on printed circuit boards that simply had more conductor for the electrons to flow through. Many audio designers maintain that “If ICs are so good, why don’t you see them in any of the finest audio amplifiers?” Fact is that the transistor has rivaled tubes in sound quality while being a far more efficient device. The IC might never be able to produce enough current reliably to be considered for amplification but it has a home in many other low current applications like mixing consoles and processors of most every type. In plain English this means that today you can still find “state of the art” analog studios and sound reinforcement systems that can sound amazing. Analog is not perfect. It has noise, it has heat loss, it has distortion, but it is easy to listen to.

Reason 2 – The digital revolution has moved so fast that not enough attention has been paid to how the product sounds compared to how many functions it can perform. The current digital mixing consoles are sold on their features. Further proof of this is the re-emergence of tubes in combination with transistors and ICs in processors designed to add warmth to the sound. If you are continuing to doubt the above, buy your next CD from the store then download the hit song from the Internet, burn a copy of it and listen to them both in a high-end, hi-fi shop on a set of speakers worth over $3,000. The difference between the two discs will astound you.

Reason 3 – People. A Front of House engineer that has been on tour with a metal band for the last 10 years probably does not hear well anymore. Conversely, a graduate of a production school program has not had enough hands on experience to make a good recording or handle a live show. A person can read all the books on golf ever written and not break 100 playing the game. You have to do it to be good at it! It will not hurt if you have a solid understanding of acoustics and electronics while you are at it. I have seen PA technicians put speaker boxes out of phase, have no idea about time alignment of drivers vs. delay lines vs. delay effects. Front of House sound “engineers” who must have gotten the gig because of how they bop their heads in time with the flashing red lights on the console and studio engineers who got their gig because of how cool they were to party with.

Ted Barker is an independent audio consultant and production specialist affiliated with Show Pro in Toronto. He can be reached by e-mail at tbar61@yahoo.co.uk.

Sound For Picture: Sound Design … Realistically

Wednesday, December 18th, 2002

The term sound design is often misused. Typically it conjures up visions of science fiction or fantasy films that feature people, places or things that do not exist in our reality and thus need to have their own sounds created (or “designed”). However, the term sound design is more appropriately used to describe an all-encompassing, top-to-bottom, start-to-finish overview of what a film is going to sound like. From that point of view, most supervising sound editors who work closely with the director and picture editor of a film project can be considered sound designers, but many of us prefer to reserve that term for a select number of our peers. Indeed, sound design is not the domain of the synthesist or plug-in junkie. The best approach to sound design is considering what sound is needed during every frame of a film, and that process is best started by looking at what is in each of those frames at any given time. There is a commonly used, self-explanatory phrase amongst sound editors that reads, “See a dog, hear a dog.” My challenge to all editors (or designers, if you must) is to go a step farther – “See what kind of dog? Well, hear that kind of dog.” This is a deceptively complex task at times.

The most successful track for a feature is one that does not distract from the entire viewing experience, so we must endeavour to make our tracks fit seamlessly with the images on the screen. That is not going to be achieved by, for example, cutting the sound of a muscle-car engine for a Reliant K-Car. You say that muscle car engine is the only one you have in your library? Well, time to expand your library! Go out and shoot (record) one. You will only ever be as good as your library, and note that off-the-shelf libraries will rarely have exactly the sound that you are looking for.

Now, of course, it may be that in the script for the film, a scene is described where a throaty V8 engine block and exhaust system is fitted (somehow!) into a K-Car. Well, the supervising sound editor who has been in touch with the director from the pre-production planning stage through to the last day of the printmaster will have to figure out how to pull this off in the track. In short, they will have to design the sound of this vehicle…

Stephen Barden is a Supervising Sound Editor for Sound Dogs Toronto, who recently brought home a Genie award for their work on the film Treed Murray. The company also recently completed work on Men With Brooms, which had the largest theatrical opening for a Canadian film in history. You can contact Sound Dogs at (416) 364-4321, info@sounddogstoronto.com.


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