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View Full Version : Lecture 1 - Noise Control in Audio Systems


Andrew
04-20-2009, 07:18 PM
Unwanted noise can appear anywhere along the entire recording process. From the very construction of the studio, to the final mixing and mastering procedures of the track. It is therefore extremely important to identify areas where incidental sound may occur, and make necessary precautions to prevent it.

One of the first issues to consider is the studio location. Whether if the owner is building a studio from scratch, or refurbishing an old office building, some research is required on the area in which the studio is going to be. When deciding on a location, the key aspect to consider is the environmental sound sources in the area. For example, if the location is in an urban area, you would need to take into account things such as rush hour traffic, train stations and airports nearby. If not considered, these factors may become problems which would affect the quality of recordings that come out of a studio (e.g. A plane going by the studio during an important take). Therefore, selecting a suitable place to build a recording studio is the first step in preventing unwanted noise.

When considering noise prevention, another important issue to consider is studio architecture. Owners are faced with two choices when thinking about investing; either to convert an existing building or build a studio from scratch. The obvious advantage of using an existing building are lower costs. However, building from scratch allows the owner to specify what he or she wants. Also, although it may seem easy, converting an commercial building into a recording studio is actually quite complicated, since a lot of buildings simply can not fit the specifications of a studio; i.e. space, building materials and foundations.

Building an entirely new studio allows a large degree of specification. It opens up a variety of ways to acoustically treat and soundproof a studio, ultimately allowing greater noise control. One of the key methods of preventing external sound from entering the studio is by installing a floating floor system. A floating floor is when the surface layer rests on a resilient layer which isolates it from the base floor on which the building is built. This resilient layer acts as a shock absorber which stops sound waves traveling underground and into the studio. As for soundproofing other surfaces, most professional studios use an acoustic membrane called dB-Block; a thick sheet of PVC material designed to block sound from transmitting through the surface its attached to. Another way of soundproofing is by installing Super Quilt between wall cavities.

Although a studio may be thoroughly soundproofed from outside noises, recordings may still be hindered by the sound of machinery operating in the room. These include equipment such as computers, fans, tape machines etc. To solve this problem, studios often have a isolated ‘machine room’ for storing the above apparatus.

Studio design plays a large role in noise prevention. For example, the way in which the air conditioning system is designed may help in minimizing unwanted noise. Once you have musicians playing in an enclosed room, you have to think about air flow inside the studio. Large AC units are incredibly noisy; this problem can be tackled by putting them in the machine room. However, air vents also make noise, and to lessen the sound of airflow, vents can be shaped in 90 degree turns so that the frequencies in the airwaves break up.
(http://www.customaudiodesigns.co.uk)

The size and shape of a room determines its natural resonances. Having too many reflecting surfaces or too little can add incidental sound, and ultimately ruin the recording. Any good studio should aim to combine a collection of reflective and non reflective surfaces. Eastlake Audio is an acoustic consultancy set up in 1975. They created their own unique studio design known as the ‘Eastlake design’, which many other studios around the world copied by the book. The Eastlake design was popular because of the incredible quality of sound it produced, the problem with that was when the recording was taken elsewhere to be played, the quality decreased dramatically. The Eastlake design is a good example of how important studio design can be in terms of controlling noise in recording.

There are several important aspects to take into account when considering the studio layout. Power circuitry and the mains should be laid out away from any audio circuit. This is because magnetic fields are generated around the mains when electricity is running through them. These fields affects audio signals if cables are placed too closely together. Florescent lights also should not be used any where near audio devices since they draw a large current when they turn on, and thus interferes with the equipment.

To specify a certain sound, or to even get rid of unwanted noise (e.g. reverb), a number of devices can be used to acoustically treat a room. Acoustic diffusers are used to scatter sound waves. A common diffuser is Pyramid Polyurethane Foam, which can be cut into a certain size and glued to a wall. Sound absorbers are used to absorb sound waves to reduce the noise level. Fabric panels are cloth wrapped fiber glass boards, usually used in most studios to absorb sound.

Finally, with all the precautions made to ensure that no unwanted sound will appear during a take. It is essential that during the recording process itself, noise control is managed effectively. For example, the number and the direction of the microphones is important when it comes to noise reduction. If cardio microphones are set to omni-directional, or one of the mics are pointing away from the sound source, they might pick up environmental noise.

One of the most problematic noise control issues for studio engineers is when vocal popping occurs. This can be fixed by putting a pop shield in front of the vocalist, moving the microphone or pointing it away from the source.
A good recording suggestion is to get as much level or volume on the mixing desk when monitoring, without overdriving with the gain as it causes distortion. Another pointer on noise control is to set up some studio rules which make sure people in the studio don’t interrupt a recording. For example, nobody is allowed into the live room when the record sign is on, or mobile phones and keys are not allowed in the live room.

At the end of the recording process, mixing and mastering plays a key role in noise reduction. Dolby NR is the shortened name for a number of noise reduction systems which Dolby laboratories Inc. created. These noise reduction systems were developed for the use of analogue magnetic tape, specifically targeting background tape hiss. The Dolby systems work on compressing the dynamic range during recording, as to lower the noise floor, then expanding the dynamic range during playback. For the professional market, Dolby developed Dolby A and SR, which can only be found on specialized audio equipment. To minimize unwanted noise on a track, the audio engineer should incorporate the Dolby system in the final stage.

copyright - Andrew Chu music lecture series written in 2009

Gray Gray
04-21-2009, 08:07 AM
lol so this is what you do instead of working on your presentation

but pretty informative you gonna put a floating floor in the apartment ?

Andrew
04-21-2009, 10:27 PM
yea.. lets deck it.

Racho
05-04-2009, 08:31 PM
Okay...that was a very thorough lecture but it didn't answer my question. I guess I have to elaborate on my issue.

The acoustics of my room is fine, but when I have my laptop's AC plugged into the circuit of all my equipment (mixer, etc) there is a staticy noise that's generated by the power supply coming from my laptop. Only when I unplug it does it go away.

Now, I want to be able to record stuff without that electric interference with my laptop plugged in because...well it's just silly to have to wait for my battery to drain out in the middle of a session, you know?

SO do I have to get something...like a resistor/transformer or something to plug my audio cables into?

erkah
05-04-2009, 10:47 PM
There are several important aspects to take into account when considering the studio layout. Power circuitry and the mains should be laid out away from any audio circuit. This is because magnetic fields are generated around the mains when electricity is running through them. These fields affects audio signals if cables are placed too closely together. Florescent lights also should not be used any where near audio devices since they draw a large current when they turn on, and thus interferes with the equipment.[/I]

andrew doesnt write anything that doesnt cover all aspects. fucking genius ! jeesus racho

Andrew
05-04-2009, 11:26 PM
On top of moving the audio equipment away from the power source you should get an interface but you mentioned a mixer you have which shouldnt do what youre desrcbing if it has a usb or firewire which you plug into your computer (acting as an interface). But i have a feeling you might be plugging your mixer outs into your cumputers input jack. i dunno.

Mayb it would help if you posted a picture of your set up then i can really see what youre taling about. I need to know if everything is plugged in to the right places and what brand and models you have?