Archive for the 'Engineering' Category

Impedance, Hi-Fi, Headphones and Guitars

Impedance is an important part of audio technology, all the way from plugging your guitar into your amp, your amp into your cab, the cabinet microphone into the preamp and all the downstream connections, both digital and analogue, right the way to your listening experience, from speakers to plugging headphones into your mp3 player. However, how much do we know as producers and music listeners, and how much do we need to?

In all actuality, most of us don’t really need to know that much about it, previous generations of telecom, audio and electrical engineers have addressed a lot of the issues for us and, generally, if we plug something into something else, everything has been designed so that it will just work. There may, however, be a couple of things you may want to consider…

What is impedance?

For those of an electrical persuasion, impedance (Z) represents the total resistance of a particular circuit including, not just the resistors, but also the resistive contributions of other components such as capacitors and inductors. Like resistance, it is measured in Ohms. Voltage (V), current (I) and resistance (R) are related following Ohm’s law: V=IR; power (P) is the product of the voltage and the current so P=VI or P=V^2/R if we do a bit of substituting and rearranging. From that, we can see that resistance/impedance can affect our power output. And that is probably as far as we need to go here.

What does this mean for my hi-fi?

Most hi-fi separates equipment that connects using RCA/phono connectors has been designed with appropriate output and input impedances, so there isn’t usually anything to worry about. However, there might be one area where it pays to think about impedance: you can generally ignore marketing copy that tells you to spend a fortune on hugely expensive speaker cables, for most purposes, using thick, 2-core mains cable will be fine. What you are aiming to do is to reduce the resistance of the cable to ensure maximum power transfer to your speakers. Resistance is proportional to the length of the wire and inversely proportional to the cross-sectional area, the thicker the wire, the lower the resistance. The cheap doorbell cables that come with a lot of mini systems is often quite high resistance, and you lose a lot of the power as heat. Most hi-fi separates equipment that connects using RCA/phono connectors has been designed with appropriate output and input impedances, so there isn’t usually anything to worry about.

What does this mean for my headphones?

Something you may have seen in the specifications list while headphone shopping is the impedance rating. Generally speaking, higher impedance headphones will be quieter for a given volume setting on your device than lower impedance headphones. However, you do need to consider the efficiency of the driver (you may see it in the specifications as a number followed by dB/mW). Generally though, if you have your mp3 player at 100% volume with the included earbuds (possible around 16 or 32 Ohms, you’ll probably deafen yourself, but plug in some 250 Ohm ‘phones, and you may find you’re able to listen quite comfortably. You’ll also draw less current (as V=IR), so the battery might last longer, but remember you’re trading off volume: you don’t get something for nothing.

Higher impedance headphones are often used for more ‘professional’ audio applications. The increased number of turns of wire can lead to a better ‘motor system’ in dynamic headphones, improving the general sound; also, the reduced current draw can reduce distortion in the amplifier. So, for ‘pro’ applications when you’re plugged into a powerful amp, high impedance is the way to go, for portable devices go with low impedance if you like volume.

What does this mean for my guitar?

If you’re recording your guitar DI, then make sure that you are plugged into a high-impedance (Hi-Z) input. A good rule of thumb is an input impedance of more than ten times the output impedance. Guitar pickups usually quote the DC resistance figure (there is a lot of wire when you start to add a lot of turns!) and are also inductive. Direct inputs for guitars are often rated to 1 mega ohm and higher to present a large load. Additionally, make sure that you use a reasonable quality guitar cable, as some cables can exhibit sufficiently high capacitance to cause problems. And what are these problems? A loss of high end frequencies (the output impedance and cable capacitance act as a high-cut filter) and a reduction in the guitarist’s beloved sustain.

The other area the guitarist needs to pay attention is when plugging a speaker cabinet into their valve amplifier. Valve amplifiers can be very sensitive to inappropriate loads on the output transformer. Without an appropriate load on the secondary coil, the energy in the magnetic field of the primary coil can’t be completely transferred, collapses back and sends that energy back to the valve as a ‘flyback’ voltage. This is usually not good. For that reason, use appropriately rated amps and cabs (a number of amps have different rated outputs for connecting to different cabs) and contact the manufacturer if you are unsure.

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Deadmau5 says: “We all hit play”

Whether you are a fan of Deadmau5 or not, his success and high profile mean that people to tend to take notice when he says something, particularly if that something may be seen as courting a bit of controversy.

Deadmau5’s recent comment in his united we fail blog post regarding big name EDM djs and producers not really doing much more than hitting play for their live sets led to a flurry of opinions on Twitter, followed up with plenty of articles and blog posts. Here’s mine.

First and foremost, as I’ve said in a couple of previous blog posts (here and here) all I care about is the music; if all you do is press play, I’m not really going to complain, just keep the good tunes coming. As a solo EDM producer, my live sets in the past have been based on triggering pre-programmed clips in Ableton Live using a Livid Block controller, bringing pre-made kick loops, basslines etc. in and out. I did start to get a bit more sophisticated when I got my Machinedrum and then my Monomachine, but, for me at least, trying to program sounds in real-time just slowed the development of the set right down. I’d rather have more pre-made sounds and loops, and keep things moving along.

A lot of the comments on Deadmau5’s blog posts seem to be mixing up live sets and dj sets; I don’t think Deadmau5 was suggesting that djs turn up with a prerecorded 4 hour mix and hit play. However, I do disagree with his comment about beatmatching not being a skill. There is more to it than ‘counting to 4’, although it is a skill that most people can learn quite quickly with practice; take a look at this episode of Faking It (may be geographically restricted).

That being said, I have no problem with people just hitting the ‘sync’ button. I learned on vinyl, but those sync lights are always glowing on my X1. All the modern developments in technology simply change what the digital dj can do with their time; they can remix tracks on the fly and start to blur the line between a live performance and a dj set.

All in all then, what difference does Deadmou5’s blog post make to the world of music? Probably none. While a bunch of people were arguing and debating his comments, they were mostly djs, producers, music magazines or blogs. Will his comments stop people going to his gigs or end the continuing penetrance of David Guetta into the pop charts? I doubt it.

Going Live- PA and performance sound for the DJ

Now, given that this site is predominantly about house music, I don’t want to head into ‘mobile disco’ territory here. If you’re playing music out, then chances are that you are plugging into an existing system in your venue. If you’re playing big clubs, there will already be an installation waiting to go, and all you need to do is get set up with your tunes in the booth.

What I want to talk about here, are some of the situations in which the deep house dj might find themselves, where you are playing in small bars, really providing a background soundtrack for the night, rather than taking over the entire room. And it is these situations that can often require a bit more thought and preparation.

First of all, make sure what is expected of you and be clear on what your role is for the night. Talk to the manager and try and get a feel for what sort of atmosphere they want for the venue. If it is a bar, with people sitting talking, think about your volume carefully. I have heard a lot more people complain that the music is too loud than complain about it being too quiet.

Find out (ideally several days in advance) what the venue’s music setup is and work through a checklist of questions:

Do they have a built-in set up with an amp you can plug into direct from your mixer?

What type of connections?

How far from the amp will your setup be?

How long do your cables need to be?

How is the in-house system set up? Is it summed to mono or does one part of the bar get the left while another gets the right? (This actually seems to happen quite a lot…)

In some venues that are basically bars, there may be a small space suitable as a dancefloor, but without additional sound reinforcement there. One solution I have used in the past is to use a single powered PA speaker on its side, much like a monitor wedge for a foldback mix on stage. Many modern PA speakers are designed so that they can be turned on their sides like this and angled up.

In the case of deep house music, you can’t really skimp on your low frequency extension, so look for speakers that extend down to 50 Hz or below. In a lot of cases, this means looking at 15″ woofers supplemented with a high-frequency horn. Normally, this would cause problems as, once woofers get to above 10″ or 12″, the cross0ver frequency ends up in the middle of the vocal range, reducing intelligibility. However, for most styles of EDM, this shouldn’t cause too many problems, as the rest of the venue system should cover this range well, and the point of this speaker is purely to supplement the bass frequencies in one specific area.

You will also need to consider how to add this additional speaker to your setup. If your mixer has an additional set of outputs, you can sum the L+R pair using appropriate cables to your powered speaker. If not, using splitter cables is perhaps not the best option. If you use one pair of outputs to feed multiple destinations, you will change the impedance load seen be that output, this will attenuate the output, with the amount of attenuation varying by frequency. If your situation requires splitting the signal, consider using an inexpensive small-format mixer, most of which will offer multiple outputs in the form of main, control room, tape outputs and auxilliary sends. An additional useful purchase is a stereo graphic equalizer, allowing you to tailor the sound to the characteristics of the room. Remember that if you soundcheck early, the sound of the room will change as it fills up with people.

Perhaps the most useful tips are the basics: do your homework and find out about the venue system; take many more cables than you need, as well as a box full of adapters; ‘Greal’ your setup, using different colours of electrical tape to label your cables so you can quickly find your way around what can quickly become a complicated nest of wires; buy the best cables you can, the quality of the wire isn’t as important as the connectors and good ones will survive a lot more plugging and unplugging; always carry duct tape and a good few electrical extension cords and multiways.

Hopefully, in most situations when you dj out you won’t have to worry too much about the setup, and any additional equipment you add won’t be nearly as complicated as if you were engineering a live band performance and having to worry about monitor mixes, stage boxes, phase issues etc. However, reading about large concert live sound engineering is never a bad way to spend your time, and it’s always better to know a little too much than not quite enough!

Audio ‘Engineering’?

In the April 2012 issue of Sound on Sound, the Sounding Off article –a regular column in which people can raise issues and air their thoughts- was written by Jez Wells, a lecturer in music technology. Jez currently has a fellowship with the Royal Academy of Engineering and is interested in collating the training, experience and skills that those who might currently be called ‘audio engineers’ have. It is an interesting read and makes some interesting points. You can find some of the responses to his column on his blog, and they do make interesting reading. Below are some of my thoughts (you might want to read the column first!):

My training is in research science, but I’ve always had a keen interest in music; starting from the childhood piano lessons, through playing guitar in indie bands, until I discovered deep house music and moving more into production and putting together a home studio. I was an assistant professor in viral immunology, but now work solely on music.

To begin with, I have no problem with the use of the term engineer in an audio recording context, regardless of whether someone has a degree or attained chartered status. You can be a great artist without going to art college, and look at the great science that has been done in the past by hobbyists, and the clergy in particular.

I also think that the quote in the article that said “the audio ‘engineers’ you describe are generally not scientifically trained” was perhaps off the mark. I don’t know of any engineers who are scientifically trained; that is not their job, and it shouldn’t be.

Science is an abstract concept, which uses experiment to derive a set of conclusions, which establish a working theoretical framework. Engineering is concrete; engineers take this framework and apply the knowledge to a tangible output. The scientists come up with the rules of fluid dynamics, the engineers build the plane, the scientists work out the laws governing transmission of forces, the engineers build the bridge. Building a bridge is not a place for experiment.

As for the comment about miking a guitar amp, for from being non-scientific, that is the essence of scientific discovery. Pure experimentation is what science is. If you look at the philosophy of the scientific method as put forward by people like Karl Popper, knowledge can only come through experience. If you don’t try that other mic at that other distance at that particular angle off the axis, you can’t know if it will sound better or not.

The major sticking point I see with the term ‘engineer’, is that is purely, and perhaps arbitrarily used to define the people either side of the glass. You can make a very convincing argument that hearing a guitar part and knowing that it needs a 3 dB peaking cut at 2.6 kHz and that compression from a Distressor will sound better than from an 1176 is an artistic skill, rather than an engineering one.

My own personal thoughts are that the recording engineer is artist, engineer and scientist; it takes intuition, technical knowledge and knowing how to experiment to do the job. Engineer is just a job title. They may not be able to play the musical parts, they may not be able to build a mixing desk, they perhaps inhabit the middle ground, maybe they should be ‘artineers’…


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