1. Expression with sound and voice
Sound can tell us things that words on paper cannot. The same sentence "I am fine" can sound happy, tired or angry. That difference comes from the voice: how loud, how fast, how high, and where the speaker pauses.
Four kinds of sound content
- Speech: a talk, a news reading, a voice-over (the voice you hear on a video).
- Music: gives mood and rhythm.
- Sound effects: a door, rain, a bell. They tell us about a place or an action.
- Silence: a short pause also says something. It gives the listener time to think.
Why choose sound?
Sound works when eyes are busy (driving, cooking), for people who cannot see well, and for feeling. It is weak for maps, tables and long numbers, where a picture is better. Good voice work is clear: not too fast, one idea at a time, and no background noise.
2. How sound becomes numbers
Real sound is a smooth wave in the air. A microphone turns it into a changing electric signal. The computer then samples it: it measures the height of the wave many times each second and writes each measurement as a number.
- Sampling rate: how many measurements per second. CD quality uses 44,100 per second (44.1 kHz). Speech can use less, music needs more.
- Bit depth: how finely each measurement is written. 16 bits gives 65,536 possible heights.
- Waveform: the picture of all those numbers. Height = volume. Number of waves per second = pitch.
More samples and more bits sound better but make a bigger file. One minute of CD-quality stereo sound is about 10 MB.
3. Editing sound and voice
An audio editor shows the waveform. You can select a part and change it.
- Trim or cut: remove silence, coughs and mistakes.
- Fade in / fade out: raise or lower the volume slowly so the sound does not start or stop with a click.
- Volume or normalise: make loud and soft parts balanced.
- Noise removal: reduce a steady hum such as a fan.
- Equaliser (EQ): make low or high sounds stronger or weaker.
- Mixing: put several tracks together (voice, music, effects) and set each level. A common rule: keep the music lower than the voice.
Non-destructive editing keeps the original file safe, so you can undo. Always keep a copy of the raw recording.
File types
WAV keeps every number (big, best quality). MP3 and AAC throw away sounds people hardly hear to make small files (compressed, "lossy"). Record and edit in WAV, then export to MP3 to share.
4. Producing sound and voice content
Producing means making a finished piece for an audience, for example a podcast, an audio guide, a radio ad or the sound for a video. Follow these stages.
- Plan: who will listen, what do they need, how long? Write a script and a list of sounds.
- Record: use a quiet room, keep the microphone a hand-width from your mouth, do a test, and record extra takes.
- Edit: cut mistakes, clean noise.
- Mix: balance voice, music and effects.
- Export: save as MP3 or AAC with a clear file name.
- Check and share: listen on a phone and on a speaker, then publish.
Rules to follow
Ask permission before using another person's voice. Use music that is free to use or that you have a licence for. Credit the people who helped.
Try it
At home: record yourself reading the same two lines three times: calm, excited, sad. Listen. Which parts of your voice changed? Now use a free audio editor to cut the silence at the start and add a 1-second fade-out. Compare before and after.
In the 3D: before you move the Volume slider, guess what will happen to the wave. Then check.
Key formulas and definitions
- Volume = height of the wave (amplitude)
- Pitch = number of waves per second (frequency, in hertz, Hz)
- File size = sampling rate × bit depth × channels × time (in bits)
- CD quality: 44,100 samples per second, 16 bits
Worked examples
1. In a waveform, the first clip has tall waves and the second clip has short waves. Which is louder?
The first clip. Height of the wave is volume, so tall waves are louder.
2. Clip A has 200 waves in one second and clip B has 400 waves in one second. Which has the higher pitch?
Clip B. More waves per second means higher pitch. B is twice as high as A.
3. You record 10 seconds of mono sound at 8,000 samples per second and 16 bits. How big is the raw file?
Bits = 8,000 × 16 × 1 × 10 = 1,280,000 bits. Bytes = 1,280,000 ÷ 8 = 160,000 bytes, about 160 KB.
Common mistakes
- Thinking louder means higher pitch. Loud is height; high pitch is the number of waves.
- Editing the only copy of the recording. Always keep the raw file.
- Making the music as loud as the voice, so the listener cannot understand the words.
- Saving every working copy as MP3. Each save loses a little quality. Work in WAV, export MP3 at the end.