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Concepts for Home Recording

here is a classic old film on soundwaves
this is a chart showing the physical size of audio waves

Microphones  

Dynamic mikes –

These are mostly designed for stage use and are not really sensitive enough for recording except for percussion or close vocals. They need no power supply as the signal is produced by a wire coil moving over a magnet.

Condenser and electret condenser mikes –

These are a very sensitive mike powered either by phantom power (from the preamp) or by a battery. The large diaphragm (around 25mm) version is used for vocals and a whole range of instruments.

The small diaphragm version (around 10mm) is usually a small cylinder and is used for very accurate top end on string instruments and also in stereo pairs for drum overheads etc.

Ribbon mikes -

The moving component of this type is a super thin aluminum ribbon about 50mm x 5mm x 2 microns. The ribbon is corrugated and just one pop from a vocal can stretch it, ruining the tone. The ribbon then has to be retensioned.

These are excellent mikes that are mellow but very sensitive. They require special care and always have to be stored in a case, as just closing a door can create a pressure wave that will damage the ribbon. They also have low output which means they need a high gain preamp or even an in-line preamp.

There is a new generation of ribbon mike which doesn't have these drawbacks but they are not cheap.

Basics for Microphone use

Proximity -

The tone of a microphone changes as you get closer to it. Mostly the low frequencies increase in relation the higher ones. You can use this "proximity effect" to get the sound you want. Keep in mind that as you get closer the dynamics and vocal popping increases. Using a pop filter (or some nylon stocking spread over a wire loop) in front of the mike is a must for close miking vocals. Learning to turn your head when you hit a loud or high note can be very useful.

Guitars -

Avoid open sound holes. Placing a mike in front of a guitar sound hole will allow the body frequency of the guitar to dominate the sound. (which is a bad thing) Using the mike at an angle to the guitar face (10 to 15 degrees) and pointing it at the area between the sound hole and the neck is a better practice. Stuffing a towel in the guitar is also a good way of balancing the tone.

Multiple mikes -

Mikes are often used as a stereo pair by crossing 2 mikes at 90 degrees and having the heads as close as possible. The reason they have to be close is that sound waves are spherical waves of compressed air separated by decompressed air. If 2 mikes are different distances from the sound source some of the waves will be pushing on one mike while pulling on the other. When the output of the 2 mikes is added together the result is that the frequency of that particular wave disappears. (the outputs cancel each other out)

It is very hard to hear when there are missing frequencies cause by phase cancellation, which is why there are 2 simple rules used with multiple mikes that are going into the same mix.

Rule 1 - When there are 2 mikes near an instrument. The distance of the sound source to the further mike should be at least 3 times the distance of the source to the closer mike. (This is often an issue when using 2 mikes on someone who is singing and playing the guitar at the same time.)

Rule 2 - When you are recording near a wall or a surface that can reflect sound, The distance from the sound source to the wall should at least twice the distance as the source to the mike.

Recording in a small space -

In the room you are recording in you have to be aware of what noise sources are inside and outside the room. You will not be able to remove all noise sources in a home studio enviroment. Mostly you deal with it by keeping the mike as close as possible to the sound source you want to record.

For noise sources inside the room (like a computer or other gear with a cooling fan) you need to aim the 'dead spot' of the mike towards that source. Recording mikes usually have a cardioid or figure 8 (bi-directional) sensitivity pattern. Which means that the dead spot is either at the back or at the side of the mike.

Another important consideration is the sound of the room. When you clap your hands are there any reflections? A dead sounding room is no problem as you can always add reverb. If you have audible reflections you have to consider that this is going to be there on everything you record. Sometimes you can use ambient reflections to your advantage. (Some of Elvis Presley's classics had the vocals recorded in the studio toilets as they didn't have reverb devices.)

 

Preamps and A/D Converters

These are 2 important links to getting the microphone signal to a storage device and
like the microphone, they will determine the quality of the sound.

Preamp -

There are 3 considerations for a preamp.

Power - It needs plenty of gain so you have the option of not being close to the mike.

Noise - A well made preamp will increase the volume without adding any noise to the signal.

Phantom Power - many good mikes require phantom power to make the mike function.

You don't neccessarily need to spend a lot of money to have a decent preamp but you will have to check the specs and read some reviews to make sure you are getting the best in the price range.

Analogue to Digital Converter -

The next thing that has to happen to the signal coming from the microphone is that it has to be changed from a complex waveform into a numerical representation of that waveform. The short name for this device is a A/D converter. It has 2 parameters of quality or resolution.

1st parameter - Sampling rate

This is how many times per second (Hz) the waveform is looked at and recorded as a number. The sampling rate of CDs is 44.1 kHz (44,100 samples per second) Because this is just over twice the frequency of human hearing, the highest waves are represented by only 2 points, which is rather poor definition for something as complex as a sound wave. For recording purposes it is best to use high definition as there will be a lot of mathematical processes done to the wave during processing and mixing. I either use 48 or 96 kHz depending on how much processing I intend to do.

2nd parameter - Bit rate

When the the A/D converter looks at the sound wave coming from the mike, it records the voltage as a number. The bit rate refers to how accurate that number will be. Each added bit means twice as many numbers to choose from. CDs are 16 bit but most good converters now go up to 24 bit. Once again the higher resolution will result in more accurate processing even if the end result is going to be a CD.

Types of preamp and A/D units

Although home computers have preamps and converters built in they are very noisy just from being inside a computer which has a lot of components that produce electronic noise. For this reason any quality recording requires that the preamp and converters are outside the computer.

There are some nice cheap units that put the preamp in the same box as the converters which is a great idea. The digital data is then sent to the computer via usb of firewire. I would avoid units that use usb1 because the interface has low bandwidth whereas usb2 and firewire have heaps of headroom.

I use a small mixer with a firewire output that has 10 channels in and 2 coming out of the computer. There are also some good small interfaces with a couple of mike preamps. The highest quality one for the price is probably the Emu 0404 which for some reason are not sold in Australia. This is not necessarily bad, as many items of recording gear are half the price when ordered from the US.

Another option that I don't personally have experience with is using a usb mike. These have a converter in the actual microphone and simply plug into the usb port of your computer. Originally designed for podcasting, it's a simple and cheap way to start out digital recording. There are some high resolution usb mikes beginning to appear with 24/96 A/D conversion that might be considered recording quality.

 

Computer, Software etc

Computer -

Any computer that has usb2 is more than adequate for digital audio recording. The main thing is to keep the computer from being cluttered with too much software. Regular ghosting or cleaning the registry is a good routine. Sometimes installing the whole operating system from scratch is the best way to clean a computer.

Software -

There is a lot of multitrack recording software to choose from, free and otherwise. The most important qualities to look for are:

simplicity

good visual feedback - like seeing the waveforms appear during recording

ability to use plugins - small third party inserts that can be applied to individual tracks

I have recently been using Reaper. It's a very professional, low cost program that puts many other high cost programs to shame. I won't be doing a software tutorial as this program is huge, but it's layout is well worth getting used to. An excellent user manual can be downloaded as well.

There are also some nice free programas like Audacity which are good for those who just want to get used to recording concepts.

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