ardour-tutorial/content/introduction/what-is-digital-audio/index.en.md

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+++
title = "What is digital audio?"
description = "What is digital audio?"
chapter = false
weight = 3
#pre = "<b>1. </b>"
+++
**Ardour** is a digital audio workstation (DAW). Beforing using it to record and
edit sound, it might be useful to review how digital audio works.
![analogue-digital](en/adc-dac.svg)
<!-- {{<mermaid align="center">}}
graph TD;
A(fa:fa-microphone Analog input) --> B(Analog to digital conversion)
B --> | digital numeric data, samples | C(Digital system)
C --> D(Digital to analog conversion)
D --> E(fa:fa-headphones Analog output)
{{< /mermaid >}} -->
The diagram above shows how sound travels to and from your computer. The
"Analogue to Digital Conversion" (ADC) and the "Digital to Analogue
Conversion" (DAC) are done by the sound card or audio interface. The digital
system in this case is your computer running Ardour.
## Frequency and Gain
Imagine a loudspeaker. To move the air in front of it and make sound,
the membrane of the speaker must vibrate from its center position (at
rest) backwards and forwards.
The number of times the membrane vibrates each second determines the
_frequency_ (the note, or _pitch_) of the sound you hear. The distance the
membrane travels from its resting point determines the _amplitude_ (the volume,
or _loudness_) of the sound. Normally, we measure frequency in _Hertz_ (Hz) and
amplitude in _decibels_ (dB).
![speaker membrane vibration](en/membrane-vibration.svg)
Check out the great animation on this page illustrating this process:
{{< youtube RxdFP31QYAg >}}
A microphone works like a loudspeaker in reverse: vibrations in the air cause
its membrane to vibrate. The microphone turns these acoustic vibrations into
an electrical current. If you plug this microphone into a computer's sound
card and start recording, the sound card makes thousands of measurements of
this electric current per second and records them as numbers. The number of
_samples_ (i.e. measurements) made per second is called the _sample rate_, and
the number of possible values each sample can have is called the _bit depth_.
The combination of sample rate and bit depth indicates how closely the digital
signal can reproduce the sound it has recorded.
## Peaks and Clipping
When Ardour displays the samples which have been recorded, they appear as the
_waveform_ we see below. The center horizontal line indicates the membrane of
the speaker at rest, and the _peaks_ of the waveform indicate the maximum
_amplitude_.
![waveform](en/Ardour4_Digital_Audio_Waveform.png)
If we take a waveform and increase its amplitude a lot, some of the peaks may now fall outside the range that the computer can represent digitally. The computer's inability to represent peaks outside the range of amplitude is called _clipping_, which results in a permanent loss of digital information,
as well as a change in the sound quality which is recognizable as
_distortion_. Ardour marks clipped peaks with the color red, as can be seen in
the image below.
![clipping](en/Ardour4_Digital_Audio_Clipping2.png)
In the image above, one can also see the _mixer strip_ on the far left,
which gives a running measurement of the peaks, as well as an indication
at the top of the _peak meters_ showing the maximum peak so far. The red number indicates clipping has occurred.
{{% notice tip %}}
Clipping often can happen at the time of recording if you set your microphone levels too high.
{{% /notice %}}
The range of decibels between the region's maximum peak and the clipping point
is commonly referred to as _headroom_, and common recording practice is to
keep approximately 3 to 6 decibels of headroom between the maximum of your
signal and the clipping point, with the clipping point itself being
represented as 0 dB (zero decibels). In other words, an audio region with a
comfortable amount of Headroom would have its maximum peaks between 6 dB and
3 dB.
Also, because the peaks of audio signals add together, care must be taken when
_mixing_ several sources together to keep the combined signals from clipping.
## Sample Rate and Bit Depth
To make audio playable on a compact disc, for example, the computer must
generate 44,100 samples per second. The sample rate determines the highest
frequency which can be recorded or played back by the computer. A sampling
rate of 44.1 kHz means that the highest frequency which can be represented is
just under 22.05 kHz. Since normal human hearing lies within the range of
approximately 20 Hz to 20 kHz, this is commonly accepted as a reasonable
sample rate. Other commonly used sample rates include 48 kHz (e.g.
multi-effects pedals) or 96 kHz (DVD audio).
Each sample is recorded as a 16-bit number. One _bit_ is a piece of
information which is either 0 or 1. If there are 16 bits together to make one
sample, then there are 2^16 (65,536) possible values for each sample.
Thus, we can say that CD-quality audio has a sample rate of 44.1 kHz and
a _bit depth_ of 16 bits. Professional music recordings are usually mixed
using 24 bits to preserve the highest amount of detail before being mixed down
to 16 bits for CD. Older computer games have a distinctively rough sound,
using only 8 bits. By increasing the sample rate, we are able to record higher
sonic frequencies, and by increasing the bit depth, we are able to use a
greater _dynamic range_ (the difference between the quietest and the loudest
sounds possible to record and play).
Here is a great video tutorial explaining sampling rate and bit depth in a lot
more detail:
{{< youtube zC5KFnSUPNo >}}