Acoustic Sounds - Magazine Article


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Acoustic Sounds - Magazine Article

  1. 1. Indoor & Outdoor Acoustic Sounds – A Deeper UnderstandingBeyond the basicsIndoor AcousticsThe Principles of Sound and AcousticsSound is the apparent vibration of air resulting from the vibration of a sound source (e.g.guitar sound board, hair dryer, etc). We can describe such regular vibration in terms of thesum of simpler vibrations (harmonics). In other words any periodic oscillation and henceresulting waveform can be described in terms of the sum of its harmonics. Each harmonicbeing a simple sine wave (often called a pure tone) with it’s own respective frequency andamplitude.Studio-based AcousticsWhen youre trying to set up a studio on a limited budget, its all too easy to concentrate onbuying equipment rather than spending your hard-earned cash on things that dont make asound. A little money spent treating the room in which your studio is based, however, canoften be a better investment. A lot of people find out too late that the acoustics of theirchosen room cause problems, either by colouring their recordings, distorting theirmonitoring perspective or leaking sound.Live RoomThe typical recording studio consists of a room called the "studio" or "live room", whereinstrumentalists and vocalists perform; and the "control room", which houses theprofessional audio equipment for either analogue or digital recording, routing andmanipulating the sound. Often, there will be smaller rooms called "isolation booths" presentto accommodate loud instruments such as drums or electric guitar, to keep these soundsfrom being audible to the microphones that are capturing the sounds from otherinstruments, or to provide "drier" rooms for recording vocals or quieter acousticinstruments.Dead RoomA lot of studios pride themselves in having a ‘dead’ room. What does this that mean?
  2. 2. It’s free and clear of ambient noise It has enough treatments in it to soak up any sound made in the room (so as not to hear an echo).When recording at home, sometimes it’s hard to get a dead room. Heating/AC vents,windows, neighbors, etc. all contribute to those ambient noises that you’re trying to keepout of your recording. You can also be the culprit with loose clothing, watches, a squeakychair, computer fan, and even things like moving papers around.Surface types and properties;When a sound wave meets an obstacle, some of the sound is reflected back from thefront surface and some of the sound passes into the obstacle material, where it isabsorbed or transmitted through the material. Reflection and absorption are dependenton the wavelength of the sound. The percentage of the sound transmitted through anobstacle depends on how much sound is reflected and how much is absorbed. We areassuming that the obstacle is relatively large, such that no sound passes around theedges.When a sound wave in air reaches the surface of another material, some of the sound isreflected off the surface, while the rest of it goes into the material. For example, whensound hits a wall, some is reflected and some passes into the wall.If the surface that the sound wave hits is relatively smooth, more sound will be reflectedthan if the surface is rough. For example, more sound will be reflected from a smoothwall made of mud than a pile of dirt. The reason is that the rough or porous surfaceallows for many internal reflections, resulting in more absorption and less reflection.Some materials absorb sound more than others. Drapes and ceiling tiles are used toabsorb unwanted sound and eliminate echoes. Music recording studios use soundabsorbing materials on their walls to eliminate any undesired or outside sounds, whenrecording a song.Reverberation;Reverberation is the persistence of sound in a particular space after the original sound isremoved. Originally, the studio recordings were performed through the microphone quiteremote from the sound source. This microphone, like the human ear, received the soundwaves reflected from the walls of the studio room, and enrolled it into the recording. In theway the natural reverb of the studio was preserved in the recording. The effect was evenmore pronounced, when they began to use several microphones, respectively mixed witheach other, this way even better results could be achieved.
  3. 3. Sound proofing;Soundproofing is any means of reducing the sound pressure with respect to a specifiedsound source and receptor. There are several basic approaches to reducing sound:increasing the distance between source and receiver, using noise barriers to reflect orabsorb the energy of the sound waves, using damping structures such as sound baffles, orusing active antinomies sound generators. Since the early 1970s, it has become commonpractice in the United States and other industrialized countries to engineer noise barriersalong major highways to protect adjacent residents from intruding roadway noise. Thetechnology exists to predict accurately the optimum geometry for the noise barrier design.Noise barriers may be constructed of wood, masonry, earth or a combination thereof. Ananechoic chamber (an-echoic meaning non-echoing or echo-free) is a room designed to stopreflections of either sound or electromagnetic waves. They are also insulated from exteriorsources of noise. The combination of both aspects means they simulate a quiet open-spaceof infinite dimension, which is useful when exterior influences would otherwise give falseresults. Anechoic chambers were originally used in the context of acoustics (sound waves) tominimize the reflections of a room. More recently, rooms designed to reduce reflection andexternal noises in radio frequencies have been used to test antennas, radars, orelectromagnetic interference.Outdoor AcousticsSound bites; background atmosphere;A sound bite is a short clip of speech or music extracted from a longer piece of audio. It isoften used to promote or exemplify the full length piece. It may also be abbreviated as SOT.Before the actual term "sound bite" had been coined, Mark Twain described the concept as"a minimum of sound to a maximum of sense." It is characterized by a short phrase orsentence that deftly captures the essence of what the speaker is trying to say. Such keymoments in dialogue (or monologue) stand out more strongly in the audiences memoryand thus become the best "taste" of the larger message or conversation. As the context ofwhat is being said is missing, the insertion of sound bites into news broadcasts ordocumentaries is open to manipulation and thus requires a very high degree of journalisticethics. According to the Code of Ethics of the Society of Professional Journalists, journalistsshould "make certain that headlines, news teases and promotional material, photos, video,audio, graphics, sound bites and quotations do not misrepresent. They should notoversimplify or highlight incidents out of context."In filmmaking and television production presence (or room tone) is the "silence" recorded ata location or space when no dialogue is spoken. This term is often confused with ambience.Every location has a distinct presence created by the position of the microphone in relationto the space boundaries. A microphone placed in two different locations of the same roomwill produce two different presences. This is because of the unique spatial relationshipbetween the microphone and boundaries such as walls, ceiling, floor and other objects inthe room. Presence is recorded during the production stage of filmmaking. It is used to help
  4. 4. create the film sound track, where presence may be intercut with dialogue to smooth outany sound edit points. The sound track "going dead" would be perceived by the audiencenot as silence, but as a failure of the sound system. For this reason presence is normallyrecorded - like dialogue - in mono, with the microphone in the same position andorientation as the original dialogue recording. In the sound edit, presence occupies thesame track as the dialogue to which it applies.Unwanted noise;A Noise Gate or gate is an electronic device or software that is used to control the volume ofan audio signal. In its most simple form, a noise gate allows a signal to pass through onlywhen it is above a set threshold: the gate is open. If the signal falls below the threshold nosignal is allowed to pass (or the signal is substantially attenuated): the gate is closed. Anoise gate is used when the level of the signal is above the level of the noise. Thethreshold is set above the level of the noise and so when there is no signal the gate isclosed. A noise gate does not remove noise from the signal. When the gate is open both thesignal and the noise will pass through.They are commonly used in the recording studio and sound reinforcement. Rock musiciansmay also use small portable units to control unwanted noise from their amplificationsystems. Band-limited noise gates are also used to eliminate background noise from audiorecordings by eliminating frequency bands that contain only static.Unwanted Ambience;As you edit dialogue, you’ll often need to cut out pieces of audio that you don’t want in thesequence. For example, the director may have given directions in between an actor’s lines,or the sound recordist might have bumped into something while shooting on location for adocumentary. As long as there’s no dialogue happening at the same time, it’s pretty easy tocut out unwanted sounds. If you simply delete the sound, however, you’ll be left with a gapin your audio that sounds artificial. Since there’s always a low level of background noise,
  5. 5. known as room tone, in any recording, a moment of complete silence is jarring. In order toedit out unwanted sections of audio without creating obvious gaps, it’s common practice torecord a certain amount of room tone during a shoot. The recordist simply has everyonestand quietly for thirty seconds or so, and records the ambient sound of the room. If you’verecorded some room tone during your shoot, you can capture it so that, as you edit, youhave a long piece of “silence” that you can edit in whenever you need to cover a gap in thelocation audio. If, for some reason, room tone was not captured for a particular scene, butyou have a gap you need to fill, you can try to copy a section from another clip in the samescene that has a pause in the dialogue, and paste it to fill the gap. If you have no pauses thatare long enough to cover your gap, you can try to copy and paste a short pause multipletimes. But there’s a chance that it will end up sounding like a loop, which will be toonoticeable. In this case, you can use the following method to obtain a long section of roomtone from a short copied pause in the dialogue.Wind noise (Refer to your location recordings and essay)Recorded wind noise is a blatant sign of an amateur. With just a little know-how, its entirelypossible to achieve good quality audio recordings, even with consumer-quality equipment.To prevent wind noise, all you need to do is prevent wind from striking the microphonessound element. The black foam windscreens that come with most microphones helps toreduce noise caused by mild air movement indoors. Foam windscreens are made fromspecial open-cell foam. "Open cell" means you can blow air through the foams cells. Thesecells create an airspace around the microphone, dampening the effects of air movement,while still allowing sound waves to reach the mics sound element. Foam windscreens areusually fine for use in barely perceivable wind, and they certainly do a great job ofprotecting your microphone from damage, but the surface of a foam screen is just toodense to adequately dampen the strike of wind against your microphone the way a furwindscreen does.Fur windscreensFur windscreens, when used over a foam windscreen, provide maximum wind noisereduction. A fur windscreens synthetic hairs, being a soft and pliable material, soften the
  6. 6. winds effect on the mic. The fur breaks up the wind and dampens (quiets) it. Think ofstriking a solid surface, like a door, with your hand. It would be fairly loud, almost drum-likesound. Now imagine knocking on someones door that is covered in a soft plush fabric likethe synthetic fur. Instead of a reverberating beat, your knock would be silenced by thesound absorbing outer layer of fur.