(Principles of
sound and acoustics)
Indoor
acoustics
Studio based acoustics – Sound can travel through any surface or
atmosphere. The only place sound cannot travel is a vacuum and this in not an atmosphere
at all. It actually passes through solids better than air. Sound intensity is
lost when travelling between one material and another, for example, from the
air to a wall and back. The amount of reduction (transmission loss) is in
relation to the density of the wall. The only way mute travelling sound is for
the wall to not move at all in response to the sound. Unfortunately, all walls
are somewhat flexible and any sound striking one side of the wall will result
in the wall moving in response and sound is radiated on the other side. This is
an effect called coupling. If the sound hits a resonant frequency, the wall
will vibrate a lot and boom like a drum. This often happens with loud bass.
Live room – Live rooms are designed to bounce sound around in a way
pleasing to the ear. This is similar to live music being played in an
auditorium, or just the echo produced by talking in a bathroom. This is called “reverberation” or more
commonly known as “reverb”. One of the reasons Carnegie Hall is so famous is
because of the way it reverberates the sound. It’s like the ultimate ‘singing
in the shower’ place for professional performers, singers, and musicians.
Dead room –
Dead Rooms have very little or no
reverberation of their own and are considered to be “dead” because when you
speak, that is the only sound and it is gone as soon as you stop speaking and
it instantly mutes or “deadens” the sound. The ultimate dead room is what is
called an Anechoic Chamber. It is built in a way so that it produces no echoes
whatsoever however these are usually made for scientific/measurement purposes. A
lot of music and spoken media are recorded in dead rooms, as the product is
perfectly clear with no distortions, echoes or unwanted noise. Reverb and
effects can then be added in postproduction if wanted.
In Situ Recording – this is where the sound is recorded on location. This can relate to
a lot of different forms of media such as live music, conferences, interviews,
audio books and lots more. With in situ recording, all reverberation, ambient
sounds, atmospheric sounds and distortions due to surroundings will come
through in the product. Quite often, in situ recordings will be made using
binaural techniques. Binaural recording involves using two or more microphones
to create a surround sound atmospheric affect where it sounds like it is
happening around you. A popular example is the virtual haircut seen here https://www.youtube.com/watch?v=IUDTlvagjJA
.
Surface types, properties and
soundproofing – All surface types and materials
have different absorption and reflective qualities that affect the
reverberation around them to create echoes. The materials that reflect sound
better are always rigid, smooth surfaces such as tiled bathrooms. Also, the
least surfaces there are, the less sound will be lost. Square rooms with smooth
walls are most commonly used for reverberation but hard tubing echoes most, as
it is only one surface with no angles. Softer materials with lots of angles,
such as foam, are very good at absorbing and muffling sound. Anechoic Chambers
(silent dead rooms) are constructed using lots of long foam triangles all
pointing in towards the room. These have so much surface are combined that they
are the best sound proofing technique. The quietist room in the world uses
these foam triangles, is approximately -9.4 decibels and is 99.99% sound absorbent.
Screening –
the above is an extreme example of screening. Screening is basically sound
insulation to help prevent sound escaping or reverberating from a room or area.
These screens are most commonly only a few inches thick and only a moderate
insulator however very affective sound insulating screens can be purchased and
created. They use the same basic principals as of the dead rooms and anechoic
chambers just in a less extreme scale.
Outdoor
acoustics
Actuality –
actuality is very similar to the principles of in situ recording. All
background sound, unwanted noise and distortions due to the environment must be
taken into account and will always be in the product. It is the proper term for
live recording on location.
Sound bites – these are small snippets of a larger recording. These are mostly
used in news. Sound bites usually last 10 – 15 seconds and no longer as they
are keyley used to get an important point out without losing the interest of
the audience. A sound bite must be able to get the point across and explain why
it is important without that short time and also be interesting, powerful and
convincing to get attention and be remembered.
Background atmosphere – background atmosphere is the ambient sound surrounding a point.
This is mostly needed as an element towards film. It includes background sound
such as traffic, wind, rustling, distant voices, birds etc. They are usually
recorded on their own then dubbed onto the film so the editor has full control
over the level of them underneath the main sounds such as dialogue or more
prominent sound effects. It is a term only used when the sounds are wanted.
Unwanted noise – also known as noise pollution, unwanted noise is the same sounds as
in background atmosphere however they often cause problems when recording where
you want a clean clear sound without other background sounds in the recording
as well. Even sounds as small as the hum of an electrical device can be a big
problem. With in situ recording it is not as much of a problem and to be
expected but in studio recording there cant be any. This is why studios are
sound proofed so that no outside sound can get into the studio as well as
keeping the sound inside and keeping it clear.
Unwanted ambience – unwanted ambience is where echoes are picked up which is natural
reverberation. This is why a lot of studios are dead rooms so that there is no
chance of unwanted ambience and the effect can be applied after if they want
it.
Wind noise –
as well as being one of the many things that can come under both headings
“background atmosphere” and “unwanted noise” it can also be a big problem when
recording outside as not only does it pick up on microphones, it also created a
loud rustling, banging sound when it hits the microphone. The main way to avoid
this is to use a windshield, which is the fluffy cover seen on some microphones
and often nicknamed “dead cats”. They massively reduce the amount of wind noise
and distortion when recording outside but are not sufficient to create a studio
sound.
Simulated
acoustics
Effects units – these are used generally after recording when involving vocals and
un-amplified instruments such as drums, wind and strings. If they have been
recorded in a dead room where there is no reverberation at all then they will
apply effects in postproduction to give it more feel and atmosphere that are
achieved with acoustics. These effects include reverb, distortion, delay and
echo. However instruments that are accompanied with an amp or effects of their
own, such as guitars and synthesizers, will very rarely have effects applied in
postproduction as all the effects can be applied before recording.
Processors –
these are generally pieces of hardware that are used to add effects to a sound.
Processors can be devices such as foot pedals for guitars and instruments like
that or can be used to add reverb, delay, distortion etc. to acoustic
instruments that are recorded using microphones. What they do is take the live
sound, put the desired effect on it and allows you too control how much of that
effect is fed back to the desk. They can also be separate equalisers used just
to get the required bass, treble and mid levels from a track.
Compression and limiting – when an instrument/vocal part is recorded quite often there will be
parts that go a lot loader and “scream” above the wanted level of the track.
What producers used to do is memorize exactly where these errors were and edit
the levels manually but dropping the fader quickly where the unwanted peaks
are. Nowadays it is an almost obsolete method and producers use compressors
which electronically monitors the level of the track and when the track goes
above predetermined threshold then it will automatically reduce the level down
to a lave that is also predetermined. A useful option most compressors have is
an attack, which lets you choose how quickly the compressor starts to work
which softens the level change.
Computer based software plugins – plugins are ad-ons that are compatible for a variety of different
pieces of software providing they are of a similar function. In audio and
recording, VST plugins are used and they are usually virtual instruments that
are played using a midi keyboard by drawing notes onto a track. The other
function that VSTs can have is as a virtual processor to add effects to tracks
already created. They are very commonly used to create music electronically and
also used in postproduction of acoustically recorded music of any genre.
Surround sound – surround sound is a relatively new invention in systems of audio
playback that has quickly become standard for cinemas and quite commonly used
among home theatre systems. Basically what a surround sound system does is put
the listeners/audience/viewers in the middle of a landscape of sound as apposed
to standard stereo systems that just place the sound in front of the audience.
Surround sound usually uses four or more speakers placed all around the room to
surround the audience/listeners. To get the best result from surround sound it
is good to use the binaural recording method of recording to achieve a clear
left/right/back/front effect.
Multi-channel – multi-channel recording is where you record more than two channels
of audio simultaneously so that they are synchronized with each other. This
needs to be done using recording software with compatible hardware and drivers
that are appropriate to record these.
Pitch –
pitch quite simply means how high or low the sound of the note played/sang is.
As the vibration of an object creates all sound, whether that is vocal chords,
strings, reed or a speaker, depending on the material, size and tension of the
medium that is vibrating, the frequency of the sound wave given off will vary.
Small, tight, hard mediums will give of a high frequency and bigger, looser,
softer mediums will give off a lower frequency. The higher the frequency of the
sound wave, the higher the pitch of the note and vice versa, the lower the
frequency of the sound wave, the lower the pitch of the note.
Time delay –
delay is one of the most important effects and is used live and in the
recording studio. It is very simple how the effect works and simply stores the
input signal for a short time before sending it to the input or output. The signal
will be repeated a few times after it is first released from the delay effect
and will get a bit quieter each time. These two characteristics give the
effects of a diminishing echo from the voice or instrument.
