Tech Talk
Tech talk focuses on how to get the most out of your gear, and solutions to problems that you may experience. This page covers basic principles and some simple tips on using and maintaining your gear, to major modifications that you can do to boost overall performance. Your questions and feedback will help us determine the future contents. Feel free to e-mail us questions, or your own tips to be included.
Effects Processors & Pedals
Introduction
At one time or another, we’re all going to use an effects device. If we perform live, it’s usually a foot pedal, or echo unit for the PA. If we are involved in home or studio recording, we might use several effects processors at once. How we use these devices will determine the quality of the sound we produce.
Probably the first effects unit ever invented would have to be the fuzz box. It consisted of a black box with several transistors that made up the pre-amplifier with lots and lots of gain. This effectively saturated the amplifier stage and created what is known as clipping. The fuzz box was a very crude unit, and had a very thin but sharp fuzzy sound. You can hear a good example of this sound in the Yardbird’s hit single from the 60’s Over Under Sideways Down. It wasn’t long before others refined this invention and added extra bits and pieces to the original design to smooth out it’s characteristics. Other effects soon followed like the phaser and wawa pedal. These were predominantly analog devices. With the advent of digital electronics, new effects sprung up, like the digital delay, the chorus and flanger.
Today, there are multi-effects pedals available with hundreds of combinations of effects built in, or you can still get a single unit like a chorus, echo or distortion pedal. If you own several pedals, you can patch them in many combinations and get differing results. Some combinations work great, some not so great. For example, patching a distortion pedal before a wawa pedal retains it’s sustain a lot more than the other way around. Likewise, wawa patched before a delay pedal sounds more natural than the other way around. These are just examples, not rules. Experimenting with various combinations is great fun. You can come up with some really original effects, and you can’t damage anything.
A lot of multi-effects pedals available today have tried and tested patch combinations that have been made famous by various artists. You can take these patches and alter the settings to your liking, and then store them in user memory for future use. A point to remember is that the original settings remain in read only memory, and can be restored to the factory preset condition in the event that you make a mess of things, or want to revert to the original settings.
All effects devices produce some form of noise as part of the output signal. I hear quite often from musicians how noisy their pedal or effects units are, and if there is anything that can be done to eliminate it. Although we can’t (unfortunately) totally eliminate noise, there are some guidelines to follow to help reduce the noise floor as low as possible.
You may have heard of the term signal to noise ratio used amongst Hi-Fi buffs or in spec sheets. The term simply implies the ratio of signal level to noise level. In other words, if we want to get the maximum signal out with the minimum noise, we must keep this ratio as high as possible. If you’ve ever tried to use a rack mount effects unit with your guitar amp or microphone, you’ll understand the importance of this principle. The signal output for most line level equipment, which includes recording equipment and power amplifiers is 0db, or 770 millivolts. Guitars output about 100 millivolts, or around -20db, and microphones output much less - around 5 millivolts or -50db. As you can see, there is a great difference between line levels and mic levels. Now if we have a device whose specifications state that it has a signal to noise ratio of 60db at an input level of 0db, we can see that if we plug the microphone directly into this device that the signal to noise ratio is going to be 10db (60-50=10) or just under the volume of the microphone. That’s a lot of hissss.
Guitar effects pedals are designed for guitar level, that is -20db and work best at this level. Most rack mount equipment is designed to operate in different environments, and have switches to enable various input and output levels. If you are going to use one with an instrument amplifier and plug your guitar straight into it, the input and output setting should correspond to -20db. Settings other than this will contravene the signal to noise ratio and effectively increase the noise floor and may also overload the pre-amplifier resulting in a distorted sound.
Tone controls can seriously degrade the sound of certain effects simply because you are boosting or cutting certain frequencies that may add unwanted noise. Amplifiers that have effects loops built in will allow you to connect effects units after the pre-amp stage and before the power amp stage. This enables you to adjust your tone settings and overdrive levels before it enters the effects unit, thus overcoming this problem. There are usually level switches associated with the effects loop so you can match the effects unit’s levels. Remember that if you’re connecting a standard pedal, set the switches to -20db.
[ Top ]
Q: Why does my Electric guitar buzz ?
A:
In the 1950's, thirty watts was a lot of power, and electric cabling in buildings was minimal. Today, we are accustomed to overdriven amplifiers of 100 watts plus, we play in places that are a web of electrical wiring with fluoro all around and dimmers to set the mood. Hence the problem. The electric pickup is basically a coil of wire wound around a magnet. It works on the principle of a magnetic object (the steel guitar string) reacting with it's magnetism causing a re-action in it's coil. This re-action is passed on to the amplifier in the form of an electric signal where it is boosted to the extent that it has enough power to move a speaker cone back and forth to create the physical sound.
In this high-tech world, we have electrical wires that are buried inside the walls and floors of buildings. As they carry AC (alternating current), they produce their own magnetic fields which also react with the pickup. This is where the annoying buzz comes from. This annoyance led to the development of the Humbucker (hum - buck - er). It's underlying principle is based on two coils placed side by side. They both pick up the string vibration and the electrical noise, but are wired in such a way that the interference is radically reduced. This works great in practice, but has a different characteristic sound. It is fatter sounding with less brightness, but more punch. This is a desirable side-effect for heavy playing, lacking the finesse and dynamics that a single coil pickup can produce.
If you prefer that classic single coil sound, but don’t want the buzz, there is a good selection available. Seymour Duncan has been around for some time and realised this fact very well. He makes his pickups in the traditional way, uses selected materials together with careful winding techniques to overcome most of the problems, thus retaining that unmistakable sound.
Rocktown Music stock a large range of great sounding pickups including Seymour Duncan, EMG, DiMarzio, Fishman and more.
[Top]
Q: Why does my Electric guitar Squeal?
A:
Commonly known as pickup squeal when the amp is cranked up, this is raw feedback, caused by the sound from the speaker feeding back into the pickup. Although the pickup only responds to electromagnetic vibrations, this shouldn't create a problem. In fact, with a good pickup you can get great controlled sustain this way. The fact is, that most pickups when they are made, are wound loosely around a bobbin and have a lot of air between the wires. Sound by nature is compression and decompression of air. The more powerful our amplifiers, the more sound pressure they produce. The fine wires that make up the coil move in sympathy with the air vibration and in moving, create their own sound. This in turn is amplified and fed back and amplified and fed back and so forth until you end up with a loud squeal. a very piercing effect ... Jimmi Hendrix loved it ! The solution here is to prevent the wire from moving. Some manufacturers achieve this by potting their pickups in wax. this can be done to most pickups, but don't recommend that you try this yourself. It is very easy to ruin a good pickup this way. If you are experiencing squeal, get your pickups checked by a guitar repairer or technician.
EMG entered the market place with a radical pickup design to overcome all of the problems. The principle behind the design is to utilise a low flux density magnet (low magnetic strength), which is less susceptible to stray magnetic interference. A side benefit is that there is less magnetic pull on the strings, and therefore they ring on longer, and sustain better. A low-noise low-current transistor pre-amp was placed in the pickup itself and powered by a nine volt battery in the guitar cavity. This pre-amplifier boosts the otherwise low signal of the pickup, with the additional benefit of lowering the output impedance, (typically 10K ohms as compared to 500K ohms). This is a key factor in retaining signal integrity from the pickup to the amplifier, thus reducing noise even further. Another bonus of low impedance is that you can drive more pedals with less signal loss.
[Top]
Q: What's the best way of electrifying my acoustic guitar?
A:
There are several designs available, each one with it's own characteristic sound. The simplest method is to buy a clip-on pickup, which normally sits across the sound hole. It is a magnetic pickup, and relies on the steel strings to reproduce the sound. These pickups are generally speaking, micophonic to some extent, therefore pick up part of the sound thru the physical body of the guitar. Being magnetic, the sound is metallic which gives a lot of presence, but being also microphonic, adds color by way of acoustic sound transfer.
Another method is to buy an Acoustic Transducer. There are two types available. One is a stick on type, which is simply stuck on the top sounding board near the bridge by means of double sided tape. The second, and more commonly used type is fitted under the bridge, sandwiched between the bridge nut and bridge piece. It is invisible to detect, and becomes a permanent fixture. The second type has the most realistic sound reproduction and should only be fitted by a guitar luthier. These pickups can be purchased on their own, or included with an on-board pre-amp with tone controls.
[Top]
Q: How do I prevent my acoustic/electric guitar from howling?
A:
Another feedback issue. Buy a Feedback Buster, or stuff your guitar with acoustic padding.
A feedback buster is like a bathroom drain plug. It fits in your round hole thus closing it off. Sound from the amplifier is restricted from entering the body, and greatly reduces howl.
[Top]
Midi Systems
Since the advent of the computer, we have seen a great many spin-offs in the form of Electronic musical systems and equipment. Synthesisers and drum machines are just two examples. As each day goes past, we see technology advancing, and new devices appearing constantly at ever decreasing prices. Only six years ago, I remember standing in a friend’s recording studio in Melbourne. He was showing off his new Apple Mac computer fitted with a ten gigabyte hard disc that he could record directly to, together with all the settings of his motorised 32 track mixer. Cost, $250,000.00!. Today, digital hard disc recording is now within the reach of everyone. For less than two thousand dollars, you can get an eight track hard disc recording setup that rivals the quality of yesterday with ease. This article will take a quick look at what MIDI is, and what we can do with this great tool. I do not intend on getting too involved with computer jargon, but some light on the terminology will help you see how certain things are achieved. Once understood, it will take the mystery out and opens doors to wider horizons.
MIDI - which stands for ‘Music Instrument Digital Interface’ was introduced back in the seventies as a protocol to enable devices to communicate and share information. As the name infers, information is transferred in a digital format - MIDI data. The great advantage is its immunity to noise and distortion. A digital signal can collect a lot of noise, and can even get distorted - but when it arrives at its destination, the re-construction process completely disregards anything but the digital data thus assuring signal integrity.
There is a saying - Good things come in small packages. This is certainly true about MIDI. It doesn’t get any more complicated than this - Only what you do with it.
The thing to remember about MIDI data is that it does not contain any sound quality at all. MIDI data is information only. This information can describe a musical note, it can be a patch change or device select. If it describes a note, the information consists of which note (C, D# etc:), velocity (how hard the note was initially struck) duration (how long), and aftertouch. The actual sound is created by the device that receives this information. So if the recipient is a Yamaha DX-7, then you will hear the sound of the DX-7. If it's your Sound Blaster card, then it's the sounds that are built in to the card. You can connect many pieces of equipment together with MIDI cables. MIDI allows us to assign channel numbers with our data to address only devices that are listening on that channel, just like TV stations are selected by different channels. Multiple sound modules or keyboards set to the same channel and playing in unison can sound huge. By assigning unique channel numbers to each, we can address them on an individual basis. So, while one unit is sounding a note, we can transmit a patch change on another channel to another unit that is on that channel and signal something completely different.
If you’re a solo artist, and say, play the guitar, your set-up might consist of a portable computer with a sound card, or a dedicated sequencer like a Roland XP-50 or maybe a Korg i5M. You may have a guitar effects processor, an effects unit for your vocals, a Harmoniser to generate backing vocals and even some lighting that is controlled thru the MIDI interface. When you hit ‘Play’, everything works together the way it was programmed. Your effects pedal or processor can automatically select a pre-determined patch together with the vocal effects. At the first chorus, the harmoniser can be set with pre-programmed harmonies, the lighting moods change, etc... Your solo comes up - your guitar takes on a smooth distortion, the lights begin to pulsate as you reach a crescendo - the possibilities are endless!.
Most households today have at least one personal computer. Sound cards for PC’s can be bought for less than $120.00, and there is also available on CD ROM a virtual sound card for around $150.00. PC’s allow you to record, play back and otherwise manipulate music in as many ways as you can think of. The software that is available today is very easy and quick to learn, and in no time at all, you can put down ideas that can turn into mega songs. There is a great flurry of song titles available on the Internet in standard MIDI format that you can download and play with and use as building blocks to bigger and better ideas.
MIDI is not Magic - It’s a great tool at our disposal. Make the most of what is available, and you’ll enjoy greater freedom and creativity.
[Top]
PA Systems
How many of you have done gigs where the band is cooking, and, although you’ve got a 2,000 watt PA, you still can’t hear yourself or it sounds like a jumbled mess, or even worse, the management complains that ‘It’s Too Loud !’ This last complaint is a serious one in that it can be the decider wether you work there again. By understanding a few principles, you can make yourself heard by everyone clearly. Remember - If you sound good, you’re remembered. If you sound loud or noisy, you’re not.
Speaker Placement
This first tip is simple, and makes sense. By far, the most important aspects of any band, be it large or small, is where you place speakers. Place them high - By placing speakers above head height, you will disperse the sound as far as possible. Being above head height, the audience at the front will not be blasted off the floor, and you’ll be heard clearly by those at the back. This factor alone will save you hundreds of watts of power. You’ll be amazed how far just 200 watts will go.
Feedback
Before getting too involved with this very complex problem, It should be made it clear why feedback occurs. Put simply, it is signal that is being fed back into the system, from speaker to microphone, thus re-generating itself and reaches an uncontrollable level. (For this reason alone, it is important to position the speakers off axis from the microphones, or, so they will never be in front of the speakers.) Feedback usually occurs at one or two or more specific frequencies. These frequencies will vary under different circumstances, being partly due to acoustics of the room and partly speaker design. In fact, like room acoustics, most speakers are anything but perfect.
If you listen closely to different speaker systems, you will notice that they all display their own peculiar sound characteristics. Some sound very bright, some bassy and some mid-dy. If we were to draw a graph starting at the lowest note to the highest note and graph the response of these speakers, we would see peaks and troughs at certain frequencies, where the speaker responds with more or less efficiency. A perfectly designed speaker will sound perfectly flat, or, all frequencies will respond with equal intensity, corresponding to a straight line. This exists only in a perfect environment. In practice, reflective surfaces and dead spots create complex problems beyond the scope of this discussion.
As a perfect environment is not feasible, Graphic Equalisers were developed to help overcome the problem. We’ve all heard of a Graphic Equaliser. It’s one of those things with a bunch of sliders on the front panel, and labels on each one, like 50Hz and 2.2khz, and +15db along the top and -15db along the bottom. If you’re not technically minded, and, most of us aren’t, it may as well be Greek. However, this device was specifically designed to equalise the peaks and troughs in the response curve we drew in the above graph. (hence the name, Graph-ic Equalise-r) Each fader has been tuned to a pre determined frequency that can be boosted or cut accordingly. If you know what frequency is causing the feedback, it is simply a matter of pulling back that frequency.
Consequently, another use a graphic equaliser is put to is to boost the bass or treble response of a speaker system. This is fine, as long as you remember what a graphic equaliser was initially intended for. Although it has, and still is, used as a sort of Turbo Charger, it allows you to pump more power to the speakers at other frequencies and force the speakers to work beyond their capabilities. If you go too far, you can make the system sound muddy, or, at worst, blow the speakers out. - If you followed tip number one, this should not be such a huge problem, as you won’t be using mega-watts.
In most cases, however, the dominating problem of feedback eminates from the Foldback system. This is where the speakers are facing you, and the back of the microphone. This is also the place for a graphic equaliser. As the monitor system is purely for your own reference, the importance here is for yourself to be heard. Cutting back on the lower bass frequencies (which needs at least two to three times the power as mids to project) will greatly increase the efficiency of the speaker, and leave reserves of power for the mids (where your vocal range lies). This also has a calming effect on the movement of the speaker cone, thus increasing sensitivity.
As stated, most of us can't describe the particular frequency in a given situation that is causing the problem. We would need a Spectrum Analyser and a powerful computer. We are living in the 20th. century, and just such a device is available. Sabine have developed a computer program that can immediately identify problem frequencies and modify digital filters instantly to elliminate the feedback.
[Top]