Audio production for multimedia: HSC Industrial Technology Multimedia Technologies

What this dot point is asking

Audio, narration, music, sound effects and ambience, gives a multimedia product depth and clarity. NESA expects you to describe how audio is recorded, edited and produced for multimedia, including how sound is digitised, how it is captured and mixed, and how it is compressed and stored. This knowledge shapes the audio in your Major Project and is examined in the written paper.

How sound becomes digital

Sound is a continuous wave, but a computer stores it as numbers, so it must be digitised by sampling. The system measures the wave's level many thousands of times a second and records each measurement:

• Sampling rate is how many measurements are taken per second. A higher rate captures higher frequencies and more faithful sound.
• Bit depth is how precisely each sample's level is recorded. A higher bit depth captures a wider dynamic range with less noise.

Higher sampling rate and bit depth give better quality but larger files, the same quality-versus-size trade-off seen across all digital media.

Recording and microphones

Good audio starts with good recording. Microphones convert sound to an electrical signal, and choosing the right microphone and placement matters: close, directional microphones for narration to reject room noise, and appropriate setups for music or ambience. Recording in a quiet, acoustically controlled space, setting levels so the signal is strong but not clipped, and monitoring with headphones all produce clean source audio that needs less correction later.

Editing and mixing

Recorded audio is edited and mixed in software:

• Editing trims silence and mistakes, joins takes and arranges clips on a timeline.
• Mixing balances the levels of narration, music and effects so each is heard clearly, fades sounds in and out, and pans them across the stereo field.
• Effects and processing such as equalisation, noise reduction and reverberation correct problems and shape the sound.

Skilful mixing is what makes narration sit clearly over music rather than fighting it, a key quality marker.

Compression and file formats

Uncompressed audio files are large, so audio is usually compressed:

• Lossy formats such as MP3 discard data the ear is less likely to notice, giving much smaller files at some quality cost, ideal for delivery where size matters.
• Lossless and uncompressed formats such as WAV keep full quality at large size, used for editing masters.

The format is chosen for the balance of quality and file size the product needs, with smaller compressed files for fast loading in the finished product.

Common settings and why they are used

It helps to know typical industry settings and the reasoning behind them. CD-quality audio is sampled at 44.1 kHz with 16-bit depth in stereo, which captures the full range of human hearing (up to about 20 kHz) because the sampling rate must be at least twice the highest frequency to be reproduced. Speech for multimedia is often recorded at the same rate but can be delivered at lower rates to save size, since narration carries less high-frequency content than music. Bit depth governs the dynamic range (the gap between the quietest and loudest sound), so a higher bit depth means less background hiss in quiet passages. Understanding why a setting is chosen, rather than just naming it, is what earns marks in the written paper.

MIDI versus recorded audio

A useful distinction is between recorded (sampled) audio and MIDI. Recorded audio stores the actual digitised waveform, so it reproduces any real sound but produces large files. MIDI stores performance instructions (which note, how hard, how long) rather than sound, so the playback device generates the notes; MIDI files are tiny and fully editable but limited to instrument sounds the device can synthesise. A multimedia product might use recorded audio for narration and ambience and MIDI for background music that needs to be small and easily changed.

Using audio in multimedia

Audio supports a product when it is purposeful and well balanced. Narration must be clear and intelligible, background music should set mood without drowning speech, and sound effects should reinforce actions and feedback. Levels are kept consistent across the product, and audio is compressed sensibly so it loads quickly. In your folio, justify your audio choices and show how recording, editing and mixing produced clean, balanced sound that serves the brief.