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2005
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Our services include Sound Engineering, Audio Post-Production, System Upgrades and Equipment Consulting.
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Wednesday, October 1, 2014

Korg The Voice UK shares the importance of the setlist feature in the Kronos

Q. What does 'parallel compression' mean?

Sound Advice : Mixing




As a beginner, it seems that the more I explore, the less I understand. Certain techniques are referred to a lot but go right over my head. Parallel compression is something I read about that is a complete mystery to me! Could you explain what it means?



Eliza Monterosso via email

The clue to parallel compression is in the name: two signals — one 'dry', and one compressed — run in parallel to one another. This is often used with drums, as in the diagram, to blend wet and dry signals, thereby maintaining some of the original dynamics.

SOS Reviews Editor Matt Houghton replies: Essentially, this is a technique whereby you use the compressor as a send effect (you'd traditionally use it as an insert), so that the dry and compressed signals are running in parallel — just as is shown in the diagram on this page. You'd normally achieve this by taking the source track and then using an aux send control to 'send' some of the signal to another channel with your compressor on it. You might then bus both the source and compressed channels to a group channel. In a modern DAW, you could achieve a similar thing by duplicating (or 'multing') a track, but I prefer using sends, as even after edits you'll know that you're working from the same source audio. Increasingly, new compressor designs include a wet/dry blend control, which avoids all this routing and allows you to perform parallel compression on a single channel. However, you might or might not process the compressed version differently from the dry version, and a simple wet/dry control doesn't allow you to do this.



Parallel compression is often used on drums, and the technique is frequently referred to as the 'New York drum trick'. The effect can help to keep a part solid and 'anchored' in the mix, while retaining some of the dynamics of the original — and you can easily determine how dynamic the part is in different sections of the song by balancing the two channel faders. A common extension to this trick is to put a slight 'smile' EQ on the compressed drums.The clue to parallel compression is in the name: two signals — one 'dry', and one compressed — run in parallel to one another. This is often used with drums, as in the diagram, to blend wet and dry signals, thereby maintaining some of the original dynamics. The clue to parallel compression is in the name: two signals — one 'dry', and one compressed — run in parallel to one another. This is often used with drums, as in the diagram, to blend wet and dry signals, thereby maintaining some of the original dynamics.



Some engineers take the parallel compression principle much further than this, though, and you don't have to stop at a single compressor. Michael Brauer, for example, reportedly likes to send vocal parts to several different compressors and blends the results to taste. You can read more about that in a Cubase technique feature we ran back in SOS April 2009 (/sos/apr09/articles/cubasetech_0409.htm).



One thing you should bear in mind is that you need to have plug‑in delay compensation switched on in your DAW to use this technique, particularly when working with transient‑rich sources like drums. Otherwise, when the parts are summed back together on your drum or master bus, the result might phase nastily, robbing your drums of power.    

Matt Berry talks about the MS-20 mini

Tuesday, September 30, 2014

Q. Why do I need to use a DI box?

Sound Advice : Recording




I've been reading a fair bit about the best way to directly connect instruments to a PA recently, and I must admit I'm still a bit confused. My first question — hopefully the simple one — is why is it recommended that an instrument (say, a keyboard) is connected to a DI box, which changes the signal to low‑impedance/mic‑level, and then send it to the mixer, where it goes through a preamp to end up as a line‑level signal again? It seems that it would be simpler to send the line‑level signal and plug it into an insert on a channel, rather than a mic input.My second question is a bit more vague and has to do with connecting other instruments, such as a harp with a transducer and an electric violin. These obviously aren't microphone or line‑level signals and I'm not sure how to treat them. I have been advised to use an LR Baggs Para DI for the harp, which appears to be a preamp that then cuts the signal back down to mic level.



Via SOS web site



SOS Technical Editor Hugh Robjohns replies: Both arrangements will work but, unless the cables' lengths are very short, the DI route will usually provide better quality, despite the apparent illogicality!



Firstly, the fact is that all cables are capacitive, and that capacitance reacts with the source and destination impedances to form a low‑pass filter. The higher the impedances and the longer the cable, the worse that gets, curtailing the high end. So working with a low source impedance and relatively low microphone input impedance means you can pass signal over extremely long cables without problems. There are many reasons to use a DI box. For example, the capacitance of cables reacts with source and destination impedances, forming a low‑pass filter. When dealing with high impedances and long cables, this only gets worse, curtailing the high end of the signal. The relatively low impedance created when the signal passes through a DI box enables you to work with long cables without problems.There are many reasons to use a DI box. For example, the capacitance of cables reacts with source and destination impedances, forming a low‑pass filter. When dealing with high impedances and long cables, this only gets worse, curtailing the high end of the signal. The relatively low impedance created when the signal passes through a DI box enables you to work with long cables without problems.

There are many reasons to use a DI box. For example, the capacitance of cables reacts with source and destination impedances, forming a low‑pass filter. When dealing with high impedances and long cables, this only gets worse, curtailing the high end of the signal. The relatively low impedance created when the signal passes through a DI box enables you to work with long cables without problems.

Secondly, sending a balanced signal to a differential input means that RF and EM interference breaking into the cable can be largely rejected, which is very handy in a hostile and unpredictable environment in which there will be lighting interference and who knows what else. Mic signals are generally balanced, whereas instrument line signals are not.



Thirdly, most PA systems are set up with a mic‑level snake from stage to mixer, and it's just a lot more convenient, and faster, to rig to work entirely with mic‑level signals rather than a mix of mic and line.



Finally, the balancing transformer in the DI box also provides galvanic isolation between stage equipment and PA equipment, helping to avoid ground‑loop problems and potential electrical safety issues under fault conditions.

Some unusual instruments, such as harps, can be fitted with piezo pickups or contact mics, whose outputs are usually at 'instrument' level, and will therefore require a DI box.

As for your second question, regarding connecting more unusual instruments, these are generally fitted with piezo pickups or contact mics, similar to many acoustic guitars with fitted pickups. The output from the control or interface box will usually be 'instrument level', much the same as a guitar and will require a DI box again.Some unusual instruments, such as harps, can be fitted with piezo pickups or contact mics, whose outputs are usually at 'instrument' level, and will therefore require a DI box.Some unusual instruments, such as harps, can be fitted with piezo pickups or contact mics, whose outputs are usually at 'instrument' level, and will therefore require a DI box.Photo: Flickr / Alan Cleaver



A decent active DI will set you back about £100 in the UK, but many people baulk at that when they see generic 'active DI' boxes going for £20 or so. However, the difference in sound quality is often very significant, and in my experience the better boxes are built to last. If you amortise the cost of a decent box over 10 years or more, it only costs £10 a year, and that's peanuts compared to your mics and other gear.



As for recommendations, I'm a fan of the Radial J48 and the BSS AR113, but the Canford Audio Active DI box (originally designed and marketed by Technical Projects) is also excellent and remarkably versatile. The Klark Teknik DN100 is another strong contender.    

Adding a Band-Pass Filter to the Korg MS-20 Mini

Q. How should I use my new multi‑pattern microphone?

Sound Advice : Miking




Having been using a cardioid mic for some time, I've just bought an Audio‑Technica AT2050. Although my decision was partly based on the flexibility of its switchable polar patterns, I've not ventured beyond the cardioid pattern that I'm used to since I bought it. How can I use the different patterns? Are there any creative techniques I can use?



Ben Allen via email

A multi‑pattern mic, like the Audio‑Technica AT2050 shown here, provides a relatively inexpensive way to try out different polar patterns. If you already have a cardioid mic, you could use the two in conjunction to start experimenting with stereo miking techniques.

SOS Reviews Editor Matt Houghton replies: This is probably a rather broader topic than you realise, but it's great that you're showing curiosity and a willingness to learn! Generally speaking, the best thing to do is to learn through trial and error: try out the different patterns and compare the results. Even with all the theory in the world, you need to make errors in order to learn! That said, we've published several features over the years that discuss this topic in more detail (for example, there's one in SOS March 2007: /sos/mar07/articles/micpatterns.htm), and I'd suggest that you have a read of some of those.



To get you started, though, I'd recommend investigating the figure‑of‑eight pattern, which is really useful where you want to reject sounds off to the side: you point the null at the bit you want to reject, and the front (or rear!) at the bit you want to capture. Bear in mind that the trade‑off in achieving this excellent off‑axis rejection is that you pick up as much sound from the rear as you do from the front, so you either need to be working in a nice‑sounding room, and be happy to capture ambience, or to have some sort of acoustic shield placed behind it. I find that figure‑of‑eight mics often make very useful room mics: you'd set them up to pick up room ambience only, with the null pointing toward the sound source.

The polar patterns available from most multi‑pattern microphones include the three shown here: (left to right) cardioid, omnidirectional and figure of eight. The diagram shows where the polar pattern picks up sound and where it rejects it.

A multi‑pattern mic, like the Audio‑Technica AT2050 shown here, provides a relatively inexpensive way to try out different polar patterns. If you already have a cardioid mic, you could use the two in conjunction to start experimenting with stereo miking techniques.A multi‑pattern mic, like the Audio‑Technica AT2050 shown here, provides a relatively inexpensive way to try out different polar patterns. If you already have a cardioid mic, you could use the two in conjunction to start experimenting with stereo miking techniques.



If you have another cardioid mic handy, you could try Mid/Side stereo recording, with the cardioid mic (it could actually be an omni, figure of eight or anything in between, but cardioid is more typically used) pointing toward the sound source and the figure-of-eight rejecting the sound source but picking up from left and right. In this instance you record three tracks: the cardioid, and two signals from the figure of eight. Polarity‑invert (ie. flip the 'phase') one of those figure‑of‑eight signals, and route both to a group channel in your DAW, and you have a mono‑compatible stereo recording whose width you can alter by balancing the cardioid's fader with the figure‑of‑eight group fader. If this whistle‑stop explanation is a bit brief, you can learn more about the technique at /sos/feb02/articles/cheshire0202.asp.



The polar patterns available from most multi‑pattern microphones include the three shown here: (left to right) cardioid, omnidirectional and figure of eight. The diagram shows where the polar pattern picks up sound and where it rejects it.The polar patterns available from most multi‑pattern microphones include the three shown here: (left to right) cardioid, omnidirectional and figure of eight. The diagram shows where the polar pattern picks up sound and where it rejects it.The omnidirectional pattern is also potentially very useful. As this is a large‑diaphragm mic, it's probably not as true an omni pattern as you'd find in a small‑diaphragm capsule, but it should give you a much more 'honest' sound than you'd get from the cardioid pattern, so if you're looking to capture the sound you hear in the room, an omni is a good bet. Beware again, though, that this pattern picks up sound from all directions. That makes it great for one‑track‑at‑a‑time recordings (it's a good bet for acoustic guitar, for example), but you need to be in a nice‑sounding space — not too near to reflective surfaces — and it makes it a poor choice if you need to achieve separation between different sound sources.