Once upon a time, all sounds had to be ‘live’. there was no way to record anything you heard, and of course no way to play anything back either.

If you wanted to hear exactly how good Mozart was at playing the piano, or hear Mary Queen of Scots’ last speech, you’d have to be at the event in person because there was never going to be a CD of it…

Today, if you listen to a CD or a cassette or audio on a computer, you are listening to stored sound.

But how do you store sound? here’s where you’ll find out…

		Check..one two..one two… …how microphones turn sounds into electrical energy
		Turn that noise down!! how loudspeakers turn electrical energy back into sound.
		Groooovy adventures in ‘analogue’ audio
		Dig it! with digital audio modern recording techniques

Check one two…one two

Microphones are essential for two reasons - firstly you’ll need one if you want to record any sound. Secondly - they make pop stars look that little bit cooler than ordinary people.

A microphone converts sounds into electrical energy.

Sounds entering the microphone hit the diaphragm making it vibrate at the same frequency as the sound wave. The diaphragm is connected to a coil of wire that then vibrates near to a magnet. This produces an electric current that changes in exactly the same way as the frequency and size of the original sound waves.

Now that you’ve got your electric current, you can make it bigger, amplify it, and turn it back into sound through a loud speaker.

Turn that noise down!!

Loud speakers are essential if you want to listen back to any sound. They come in all shapes and sizes, from huge ones at concerts to small ones in headphones that you wear in your ear. Make sure you get it the right way round though.

Loud speakers take electric signals and turn them back into sound.

The varying electric signal flows through the coil; this produces a magnetic force between it and the magnet and so makes the coil and diaphragm vibrate. This vibrating diaphragm in turn makes the air vibrate – thereby pumping out a loud replica of the original sound!


In more expensive loud speakers there are two (or more) diaphragms. Smaller ones, which are good for the high frequency sounds called tweeters, and larger ones, which are better for the lower frequency sounds, called woofers.

As you can see, a loudspeaker has the same parts as a microphone – a vibrating diaphragm, a coil and magnet – it just works the other way round. This means that if you plug a loudspeaker into a microphone socket and shout into it, it will act as a microphone!

Groooooovy

Next time you visit your grandparents, ask them if they still have any gramophone records and watch them as their eyes fill up with tears for happy bygone days …

Records and Cassettes store analogue recordings. This means that there is a continuous, smoothly changing, representation of the electric current that was produced in the microphone.

On a record this is the actual groove that spirals all the way from outside of the disc to the centre.

A thin needle is placed into the groove and as the record spins, the needle is made to vibrate. This vibration is then changed back into the original electrical current, and then in turn into a sound

In a cassette tape, the analogue signal is stored as a pattern of very small magnetized particles (iron or chromium oxide). The electric signal is applied to a recording head (an electromagnet) that magnetises the particles into different patterns as the tape passes the head.

A play head can turn these magnetised patterns back into an electric signal when you want to listen back to the sound.

Analogue recordings are fine for limited use, but tapes and vinyl can be fragile and if listened to over and over again tend to lose quality. If you really want to dig it with recording, you’ll need to know about digits.

Dig it!

Digital recordings are different from analogue recordings because they don’t store the sound as a continuous streaming signal.

The more times that it is sampled, the better the faithfulness - fidelity – of the recording. So hi-fi is a short way of saying high fidelity - which is almost exactly like the original sound

On CD’s (Compact Discs) there are 44,100 samples every second. Think that’s good? Well, it’s the pits.

No really. Here’s how a CD works. A CD is made up of a series of pits - or bumps on a flat surface land. When a laser beam sweeps over the CD and hits a bump, it produces the binary number 0. When it hits land it produces the number 1. And this stream of 0’s and 1’s is converted back into a waveform of the electric current and then into sound.

Digital sound is much more robust than analogue recordings and is usually of a much higher fidelity.