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--- wiki:sound:basic_sound [2020/09/19 18:50]
Craig Flint
+++ wiki:sound:basic_sound [2022/10/09 13:56] (current)
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 # Under development!
-Sound is the most exciting part of the show - without it, you'd just be watching a silent movie! In StageSoc, the different types of shows will require different amounts of equipment and reinforcement. The highest tech shows may require amplification of the cast and band through the use of radio or wired microphones, whilst playing sound effects in time to the music and lighting cues, all whilst juggling additional equipment breakages mid-show with an audience cheering louder than you can make the speakers go. It may sound like living hell, but it really is very fun! Hopefully this page will break down the very basics of how sound works.
+Sound is the most exciting part of the show - without it, you'd just be watching a silent movie! In StageSoc, the different types of shows will require different amounts of equipment and reinforcement. The highest tech shows may require amplification of the cast and band through the use of radio or wired microphones, whilst playing sound effects in time to the music and lighting cues, all whilst juggling additional equipment breakages mid-show with an audience cheering louder than you can make the speakers go. It may sound like living hell, but it really is very fun! Hopefully this page will break down the very basics of how sound works. (You will also learn about ''The Game'' if you haven't already done so).
+====== Sound flow ======
+{ Sound source --> Microphone --> Mixer --> Amplifier --> Speaker }
+Sound is generated by pressure fluctuations in the air, either by part of an instrument vibrating or a person's voice box. These pressure fluctuations travel through the air to the listener's ears, or in our case, to a microphone. The microphone's diaphragm vibrates, converting the acoustical pressure fluctuations to electrical voltage fluctuations that can travel down a cable. These voltage fluctuations are very small (in the region of a few millivolts) as there is very minimal energy in a sound wave.
+Lots of different microphone signals are plugged into a device called a ''mixer'', which combines all of the input signals into a set of outputs (e.g. to feed a speaker in the room). As the voltage fluctuations travelling down the cable are very quiet, they first need to be boosted around 100x by a device built into the mixer called a ''microphone pre-amplifier'' (aka ''mic pre'', ''pre-amp'' or just simply ''the pre''). The mixer allows you to easily adjust the volumes of the individual microphones and they can also be edited e.g. to reduce the amount of bass or add effects.
+The different outputs of the mixer can be sent to different places for different purposes, for example one pair of outputs may feed the main stereo speakers in the auditorium whilst another set sends a different feed to the band members in the pit or the green room next door. Although the voltage levels of these signals are much larger than those straight from the microphone (due to the pre-amp in the mixer), they are still not large enough to drive a speaker. The signals are therefore sent to a ''power amplifier'', or just ''amp''. There are often multiple channels of amplification built into one box to save space - the most common are two or four channel amplifiers. Once the signal leaves the amp, it is powerful enough to be sent to the speakers. Some speakers have amplifiers built into them for ease of use, although these are often heavier than those without, and it can also be harder to change settings directly on the speaker if it is flown in the air. As such most of the speakers in The Annex are ''passive'' (need a seperate amplifier) although there are a couple with the amplifiers built in (known as ''active speakers''). They each take different cable types so you can't accidently blow them up.
+Sometimes, there will be another device between the mixer and the amps known as a ''DSP'', or ''digital signal processor''. This allows more adjustments to be made to the signal than can be made at the mixer, as settings to make the speakers sound nicer in the room won't need to be changed between different shows and is therefore safer to have them seperate from the easily-editted settings on the mixer.
+===== The different signal levels =====
+The different signal levels in each stage of the chain all operate at similar nominal (or average) levels and as such are given generic names. The very low voltage signals produced by the microphones are said to be at ''microphone level'', or ''mic level'' (engineers are very imaginative as you can tell...). These signals fluctuate by only a few millivolts (mV) and as therefore more susceptible to noise and electrical buzzing or hum.
+The pre-amp in the mixer boosts these signals by around 100x before editing them to a level known as ''line level''. These signals fluctuate at nominal levels of around 1 Volt, but the peaks (loudest parts) may hit up to around 10 Volts. These make them much more robust against noise and buzz.
+Some electronic equipment outputs at a level between mic and line level called ''instrument level''. These signals are normally converted to mic or line level by a box known as a ''DI box'' (stands for ''direct injection box'') which is placed in the band pit near to the instrument (normally within a couple of metres).
+The level that speakers require are again much larger than line level, and are called ''speaker level'' (imaginative again...). These are around 32V nominal but also carry a much higher current so are much more powerful.
+====== Microphones overview ======
+===== Microphone types =====
+There are three main types of microphones, called ''dynamic'', ''condenser'' and ''ribbon''. You'll mostly deal with dynamic and condenser mics in the Annex.
+==== Dynamic ====
+Dynamic mics generate the electrical signal by having the air pressure move a coil of wire back and forth inside an magnetic field. This means they are quite robust, but they don't reproduce high frequencies well and they aren't very sensitive. They are therefore best suited to vocals if they're singing into a mic on stage (like a cabaret-style show), or for loud instruments such as brass instruments. If you don't know what microphone to use, a dynamic is often your get-out-of-jail-free mic, and the industry famous ''Shure SM58'' and ''SM57'' mics can be seen across the world. Whole bands have been mic'd with these, and they'll get the job done.
+==== Condenser ====
+Condenser mics use a charged set of plates that act like an electrical capacitor (which is why they are sometimes also known as ''capacitor microphones''). The sound pressure waves cause the front plate to get closer to and further from the back plate, changing the capacitance and thus the voltage. The plates need to have different starting voltages though, so the microphone is supplied with power down the microphone cable by the mixing desk. This is called ''phantom power'' as it sends a constant 48V down the same mic cable that is sending back the signal to the mixer. {NOTE: remember to enable phantom power on the mixer if the mic needs it. There's normally a button (normally marked ''+48v'') for each channel (or a bank of channels) to turn this on. When you aren't getting any sound from the microphone, this is the first thing to check!} The mixer can remove this constant voltage from the fluctuating signal it receives from the microphone, extracting only the audio. As the constant voltage makes no difference to the sound (other than actually allowing it to make sound at all!) it gets its name of ''phantom power''. With a better sensitivity and high frequency response, these mics are most often used on quieter, more delicate sources such as the flute or violin.
+==== Ribbon ====
+Ribbon mics are rare in the Annex as they can be quite fragile. They also have a figure-8 polar pattern which is not ideal, but this is covered next.
+===== Polar patterns =====
+''Polar patterns'' (or ''polar plots'' or ''pickup patterns'') describe how well a microphone picks up sound in one direction compared to another. The patterns can vary on a scale from not directional to very directional, although there are some common patterns that are defined on this scale.
+==== Omni ====
+The first pattern is known as ''omni-directional'' (shortened to ''omni'') which means the microphone picks up sounds equally well from all directions. These patterns are not very useful for live use as they are more likely to pick up their own sound coming out of the speaker, which will be re-amplified by the microphone getting louder and louder. This is known as ''feedback'' and can often be heard as a whine and is very easy to hear.
+Radio microphones (the small mics taped onto the actors' faces) often use small omni microphones however, as they can be placed in any orientation on the actor with no difference in the sound (when they inevitably fall off mid-show and are stuck back on by the actors). They also don't suffer from any severe increase in bass frequencies as they get closer to the sound source (known as the ''proximity effect'' [see below]) which you get with more directional microphones due to more in-depth physics stuff.
+==== Cardioid ====
+The most common pattern is known as ''cardioid'', as the shape mildly resembles a heart shape. They pick up sound best from in front of the microphone and reject sound coming from behind. These work well in live situations as the back of the microphone can be pointed towards another loud instrument or the main speakers, which will not be amplified by the microphone.
+==== Super- and hyper cardioid ====
+A more directional pattern is known as ''super cardioid'', which rejects a bit more sound from the sides, but as a trade-off a ''rear lobe'' appears, meaning the microphone will slightly pick up sound from directly behind it. The point of maximum rejection is now at around 135 degrees instead of the 180 degrees (directly behind the mic) for the cardioid. This can be useful if you wish to reject sounds off to the sides more than directly behind the microphone. A very similar pattern known as ''hyper cardioid'' rejects slightly more sound from the sides at the expense of a slightly larger rear lobe.
+==== Figure-8 ====
+Finally, the pattern known as ''figure-8'' has equal sensitivity directly in front and directly behind the microphone. It best rejects sounds coming from the sides (90 degrees) of the microphone. These aren't often used in live sound, except in some specific cirucumstances such as placing between the snare drum and hi-hat to capture both with one microphone.
+==== Lobar / Shotgun ====
+One further pattern exists called a ''lobar'' or ''shotgun'' pattern, which is a combination of a super-cardioid microphone and an ''interference tube'' to further reject sounds from the sides. These are rarely used in live events (partly due to their size) but can be found in outdoor TV and film recordings as they are very directional and work well at isolating a person's dialogue from the surrounding background noise. They are easy to identify as they are very long.
+==== Proximity effect ====
+One point of note with directional microphones is that as you move the microphone closer to the sound source, the amount of bass the microphone will pick up will increase. This is known as the ''proximity effect''. The microphones are normally designed to give a flat frequency response at a stated distance (e.g. 30cm from the sound source) with closer placements giving more bass (the sound can become 'boomy') and placements further away causing a slight loss in bass frequencies. Omni directional microphones don't experience any proximity effect (which is another reason why they are often used with radio microphones on actors) whereas the most directional figure-8 pattern will experience this effect the most (the more directional the pattern, the more the proximity effect will be seen).
+====== Mixers overview ======
+====== Amplifiers overview ======
+====== Speakers overview ======
+====== Cables overview ======
-===== Sound flow =====
-Sound is generated by pressure fluctuations in the air, either by part of an instrument vibrating or a person's voice box. These pressure fluctuations travel through the air to the listener's ears, or in our case, to a microphone. The microphone's diaphragm vibrates, converting the acoustical pressure fluctuations to electrical voltage fluctuations that can travel down a cable.

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