From sound wave to signal
Sound is a vibration that travels through air as a wave. Its frequency (vibrations per second, in hertz, Hz) sets the pitch; its amplitude sets the loudness. Humans hear about 20 Hz to 20 000 Hz.
A microphone is a transducer: it changes one form of energy into another. Air pushes a thin diaphragm, and the microphone makes a voltage that rises and falls in the same pattern. A speaker does the opposite: a voltage moves a cone, which pushes the air.
This continuous signal is analogue. Vinyl records and tape stored analogue copies.
Digital audio: sampling and bit depth
A computer can only store numbers. An analogue-to-digital converter (ADC), usually inside an audio interface, measures the signal many times a second. Each measurement is a sample.
- Sample rate: samples per second. CD quality is 44 100 Hz (44.1 kHz). It must be more than twice the highest frequency you want to keep.
- Bit depth: how many bits store each sample. 16-bit gives 65 536 possible levels; more bits = less noise and more detail.
- File size (uncompressed) = sample rate × bit depth × channels × time.
Compressed formats (MP3, AAC) remove sounds we hardly notice to make files much smaller; lossless formats (WAV, FLAC) keep everything.
The DAW: tracks, MIDI and editing
A digital audio workstation (DAW) is software for recording, editing and arranging music. Free and paid DAWs, and phone apps, all share the same ideas: a timeline, tracks stacked in rows, and a mixer.
- Audio tracks hold recorded sound (voice, guitar).
- MIDI tracks hold instructions: which note, when, how long and how hard. MIDI makes no sound itself; it plays a virtual instrument. You can change the instrument or fix a wrong note after recording.
- Editing: cut, copy, loop, fade, change tempo, correct timing (quantise).
- Samplers and loops: short recorded sounds reused as building blocks.
With a laptop or even a phone, one person can now write, play, record and publish a whole song.
Mixing, effects and music in media
Mixing balances the tracks: volume faders set level, pan places a sound left or right, EQ boosts or cuts bass and treble, compression evens out loud and soft parts, and reverb adds a sense of space. Mastering is the final polish so the song sounds good on all devices.
Music technology links music to other media: film and TV scores, game music that changes with the action, adverts, podcasts and short videos. Streaming services use data about what we play to recommend music, which shapes personal taste. Listening tools (spectrograms, tuners, slowed playback) help us study music closely.
Using it responsibly
Respect copyright: ask permission or use licensed or free-to-use loops and samples, and credit creators. Protect your hearing: keep headphone volume below about 60% and take breaks.
Try it
Record 10 seconds of your voice on a phone. Then record a second track clapping a beat on top in any free recording app. Adjust each track's volume until both are clear. You have made a two-track mix.
Key formulas and definitions
- Transducer: microphone (sound → voltage), speaker (voltage → sound)
- Sample rate = samples per second (CD: 44.1 kHz)
- Sample rate must be > 2 × highest frequency
- Levels = 2^(bit depth) (16-bit → 65 536)
- File size (bits) = sample rate × bit depth × channels × seconds
- MIDI = note instructions; audio = recorded sound
Worked examples
1. How many levels can a 4-bit and a 16-bit sample store?
4-bit: 2⁴ = 16 levels. 16-bit: 2¹⁶ = 65 536 levels, so it follows the wave far more finely.
2. Find the size of 60 s of stereo audio at 44 100 Hz and 16-bit, in megabytes.
Bits = 44 100 × 16 × 2 × 60 = 84 672 000 bits. Bytes = ÷ 8 = 10 584 000 bytes ≈ 10.6 MB.
3. You played a wrong note on a keyboard. Is it easier to fix if you recorded MIDI or audio? Why?
MIDI. It stores the note as an instruction, so you can drag it to the right pitch in the piano roll. In audio, the note is mixed into the sound wave and is hard to change.
4. Why is a sample rate of 44.1 kHz enough for music?
Humans hear up to about 20 kHz. You need more than 2 × 20 kHz = 40 kHz to capture it, so 44.1 kHz covers the whole range of hearing.
Common mistakes
- Thinking MIDI is a sound recording. It is only note data that plays an instrument.
- Believing a higher sample rate makes a song "louder". It adds detail, not volume.
- Turning every track up to the maximum. A good mix balances levels and leaves headroom.
- Using any song or sample found online without permission.