Sound & Music – How Music & Sound Is Recorded & Sampling

How music and sound is recorded

Stephen Carr – Group 1

There are different methods of recording sounds and music, each with its own advantages and disadvantages. The processes to record the sound differ depending on whether it is being stored on an analogue or digital device and each provide a different quality of sound.

The phonograph was a piece of analogue recording equipment and was the first device that was capable of recording sounds and music. Invented by Thomas Edison in 1877, the phonograph reacted to the vibration of sounds in the air, which vibrated the phonograph’s diaphragm that was connected to a needle. The needle’s vibration would then record the sound by scratching a tin cylinder. The way it did this was by matching the vibration of the analogue wave; the wave’s pitch and amplitude would be measured and then scratched onto the tin cylinder. The sound was played by reversing the process; the tin cylinder would vibrate the needle, which led to the vibration of the diaphragm and then the sound being played through the phonograph’s cone.

One of the downsides to the phonograph was that the tin cylinder would deteriorate every time the record was played, eventually wearing out completely. This was because of the wear that would occur every time the needle passed over the cylinder. However, this same process would be used, albeit with more advanced technology and devices, to record sounds and music onto vinyl records.

Digital recording, on the other hand, records the sound and proceeds to turn the analogue wave into a stream of numbers and digital data. This is done with an analogue-to-digital converter (ADC). When the sound is played back, it then goes through a digital-to-analogue converter (DAC). The reason for this is because the aim when recording the sound digitally is for “high fidelity” – fidelity is accuracy between the original signal and the reproduced signal – and for “perfect reproduction”, which is the same sound every time the record is played. [1]While analogue recordings are accurate to a point, they lack the ability to produce high fidelity and perfect reproduction; the phonograph, for example, produced a very scratchy sound during playback and cassette tapes tended to produce a “warmer” sound than the original signal, which softened sharper notes.

Microphones and speakers actually use similar processes when receiving sounds. A microphone is a piece of musical hardware that can determine the frequency and amplitude of sound waves picked up in the air. Like the phonograph, the microphone contains a diaphragm that vibrates when it picks up a sound. However, when the diaphragm in a microphone vibrates, it moves back and forth past a magnet. This produces a current in the microphone’s coil, which is then transmitted to the recording equipment.

In the case of speakers, an electromagnet is used to receive the sound; a coil attached to a magnet that creates a magnetic field when an electrical current is passed through it. The coil itself behaves like a regular, permanent magnet. Effectively, this means the (mobile) electromagnet is placed in front of the (fixed) permanent magnet. As electricity pulses through the coil into the electromagnet, the direction of the magnetic field rapidly changes. In the same way that magnets attract and repel each other depending on which poles are connected, the electromagnet is constantly being attracted and repelled to and from the regular magnet, vibrating it back and forth. Much like the cone on a phonograph, the electromagnet is attached to a flexible cone – made of a material such as plastic or paper, for example – which amplifies these vibrations, pumping sound waves into the air surrounding it.

Both analogue and digital recordings have their own devices for storing sounds and music. For example, analogue recordings can be stored on the phonograph’s tinfoil cylinders, on vinyl records or cassette tapes. Digital recordings can be stored on CDs, mini-discs or as MP3s. The differences between the devices can be more noticeable with analogue recordings than digital ones, owing to the fact that digital recordings aim to have high fidelity and perfect reproduction.

One of the benefits to using a digital medium is being able to modify the song or sound to make improvements. However, this could also be seen as a downside, depending on the qualities most valued in a recording; an analogue recording, such as a tape or vinyl record, could have imperfections – the aforementioned “warmer” sound, for example, or dust and scratches causing vinyl records to skip – but it could still be seen as a more accurate representation of the sounds being produced at the time. This is due to the fact that music being tweaked or altered following the digital recording could be seen as reducing the accuracy of the original recording for the sake of “improving” the sounds.

Sampling

While an analogue recording effectively produces a constant recording of the “live” sound, exactly as it is played at the time of the recording. Analogue recording is very smooth and constant but to produce the same sound as a digital recording, it is split up into smaller parts with a measurement of how far apart these segments are. This measurement is called the sample rate and each segment is called a sample. The higher the sample rate is, the more frequently the sound is measured and the closer we get to the smooth sound of the analogue recording. For example, CD quality audio has 44,100 of these measurements every second or, to put it another way, 44.1 kilohertz (khz).[2] When played back, this sound appears to be seamless. In computer games, having a higher sample rate could take too many resources from the rest of the game and cause it to slow down. For example, a sample rate of around 90,000 hertz would take around twice as many samples, forcing the digital recording to work twice as hard. This would leave fewer available resources for graphics, animations and other features that computer games rely on.

Sample rate is not the only measurement required when recording digital audio. The volume is also measured using bit rate. In basic terms, bit rate is the number of volumes available to play the audio. So, for example, let’s say we only have two volumes available; 0 and 1. In that case, the volumes would simply be “off” and “on”, since the only choices are “no volume at all” and “turned up to the maximum”. If we have three volumes – 0, 1 and 2 – the “2” volume would not be any louder than the “1” volume in the original example. It would still be the maximum volume available to play. The same applies whether the highest number is 10, 100 or 1000. The volume doesn’t become any louder at the highest number but there is a wider range of volumes to capture; the higher the bit rate, the more accurately we can make the recording of the captured sound because we have a larger choice of volumes to choose from.


[1] BRAIN, M. How Stuff Works (2013) HowStuffWorks “Digital Data” [Online] Available at http://electronics.howstuffworks.com/analog-digital3.htm (Accessed on 13th October 2013)

[2] CONNOR, D. The Stereo Bus (2008) Sample Rate and Bitrate: The Guts of Digital Audio [Online] Available at: http://thestereobus.com/2008/01/12/sample-rate-and-bitrate-the-guts-of-digital-audio/ (Accessed on 14th October 2013)

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