How Digital Recording Works

Ever wondered how the music we record through traditional means makes it onto a computer, allowing us to manipulate, edit and export in a digital format?

Quick Soundbite

We hear sound in the ‘real world’ as vibrations that create waves of compression known as sound waves, that are interpreted by the brain as sound. When recording in a digital environment, analogue sound waves are sampled e.g. the sound wave’s values are recorded at regular intervals and stored as numbers by an analogue to digital converter (ADC). The sampling rate and bit-depth (the amount of information used to describe each sample) determines the fidelity (accuracy of the analogue to digital conversion).

The information above describes how digital devices e.g. audio interfaces and computers take an analogue signal and reproduce it digitally when recording. In the following article, we’ll take a closer look at the process, including a more in-depth explanation of sound waves, sample rate and bit-depth.

How we hear sound

Anatomy of a sound wave

As we know, sound is created when something vibrates. In the case of music production this might be a person’s vocal cords or the vibrations of the strings when strumming an acoustic guitar for example.

As the vibrations travel through the air, air particles are displaced. The patterns of displacement are what we know as sound waves.

The brain interprets sound waves as sound through the following process:

  1. Sound waves enter the outer ear and travel via the ear canal, where the vibrations are amplified
  2. The eardrum vibrates which causes the Ossicles (very tiny bones of the middle ear) to vibrate
  3. The last bone in the chain (the Stapes bone) acts like a bridge and transfers the vibrations between the middle and inner ear
  4. Fluid within the Cochlea (a spiral shaped bone of the inner ear) moves in response to the vibrations causing the hair cells contained within the Cochlea to move (different hair cells move in response to different frequencies) which converts the vibrations into electrical impulses
  5. Electrical impulses via the auditory nerve are interpreted as sound by the auditory cortex of the brain.

Digital recording definition

The Digital Recording Process

Based on the information above, you could say, we hear sound as vibrations. As sound, in a practical sense, is really just how the brain eventually interprets these vibrations.

In digital recording, the computer also has to interpret sound waves. It uses the following process:

  1. The analogue sound wave is detected by a microphone or direct line e.g. a transducer (guitar pickup or similar device that measures change e.g. in air pressure)
  2. The signal is amplified via a preamp (if required) and sampled and converted to digital via an ADC (analogue to digital converter) so the digital device can interpret the sound
  3. During playback the signal is converted back to analogue by a DAC (digital to analogue converter)
  4. The signal is then amplified, and can be played through speakers.

Sample Rates and Bit-Depth

Sample Rate and Bit-Depth

Digital devices perform this conversion process by taking samples of the analogue signal at intervals determined by the sample rate and using this information to create a digital replica.

The gray line in the example above shows a continuous analogue sound wave, while the darker line represents the interval based digital replica. The higher the sample rate and bit-depth, the higher the resolution of the digital wave and the closer in appearance to the analogue sound wave.

Don’t be confused by signals and sound waves. The term signal is often used interchangeably with sound wave. A sound wave is a term used to describe a wave of energy. A signal, on the other hand is a wave of information e.g. used to describe sound waves.

Hertz so good

Sample rates, much like frequencies (the speed of the vibration, which determines pitch) are measured in hertz. In the case of high-definition audio sample rates are typically as high, or higher than 96kHz or 96,000 hertz. This means, for every second of audio there are 96000 samples taken of the analogue signal!

Alternatively, bit-depth is the term used to describe the amount of information being taken each sample. It helps to think of bit-depth in much the same way as image resolution in digital photography. The higher the resolution, the more accurate the digital sample is compared to real life.

Bit-depth is measured in bits which are units of digital information e.g. a kilo bit is one thousand bits.

Back to our high definition audio example. DVD quality audio is typically 96kHz / 24-bit which means, there are 96000 samples taken per second, with each sample containing 24 bits of information.

Most modern home studio interfaces (devices that contain input/output, ADC and DAC converters and preamps) can record and process incoming audio at similar or higher sample rates.

But if you choose a higher sample rate this will, by virtue of the fact that more data is included in the digital signal also increase the size of your recorded audio files.

Analog recording — How it used to be done

By now you might be wondering how audio was recorded before the arrival of computers and digital recording.

Analogue recording also relies on the transfer of vibrations, much like the process between the ear and the brain.

But unlike the brain, which interprets vibrations as electrical impulses, the vibrations and values included e.g. amplitude (volume) and frequency (pitch) are transferred and a physical imprint of the sound wave e.g. the grooves in a vinyl record are created.

A similar device e.g. the needle on a vinyl record player would then physically convert the vibrations from the analogue medium into an electrical signal that could then be played through speakers.

Does analogue sound better?

You may have heard people state that their old vinyl records sound better than digital media e.g. CD’s, DVD’s and digital audio file formats.

After all, digital is merely a replica, or copy of the analogue signal being recorded, whereas vinyl for example is a physical imprint of the analogue sound wave.

This is certainly the case with compressed audio formats such as .MP3 and .AAC which are lossy formats. This means data is removed (using codecs that determine the least critical information required to replicate the original file) so the file size is smaller and more easily shared online. In this sense, we’re comparing apples to oranges and a fair comparison really can’t be made.

Uncompressed formats however e.g. CD’s (sample rate of 44.1kHz) and DVD’s (sample rate 96kHz) along with uncompressed audio file formats such as .WAV files hold significantly larger amounts of data.

However, especially in the early days of digital recording, many claimed to hear a noticeable difference. The most common complaint being that digital sounded cold and processed in comparison to the more natural e.g. less artificial sound of analogue.

In any case, how we perceive sound is subjective.

Most modern vinyl releases are taken from a digital master nowadays and artists such as Neil Young are on record as saying:

They’re only making CD masters in digital, so all the new products that come out on vinyl are actually CDs on vinyl, which is really nothing but a fashion statement.”

Neil Young

While the quote above doesn’t take into account the romance associated with vinyl, it’s a fair point and one most people are unaware of.

Advantages of digital recording

Rest assured, having recorded using both analogue (reel to reel and 4-track cassette recorder) and digital on numerous occasions, analogue is a far less efficient way to work with audio. Editing is considerably more time-consuming and difficult.

The view of people like myself is that any loss of warmth or character compared to analogue is likely to be minimal, especially when compared to the advantages of digital recording and costs associated with setting up a home studio compared to what it once was.

It should also be remembered that analogue mediums degrade, at least a little every time they are played. Which, over time also has an impact on the listening experience.

Coda

A lot has changed over the previous 20+ years with regard to audio recording technology. Much of what makes a great sounding recording sound, great has little to do with the technology involved.

And while it can certainly help to understand the analogue to digital conversion process, don’t allow yourself to get too caught up in the tech and pay less attention to the things that really matter. e.g. great songwriting, great performance and the acoustic qualities of the room you are recording in.

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