4.2.2
Audio files
Two settings do most of the work in this subtopic, and they get mixed up constantly. Sample rate is how often the sound is measured. Bit depth is how precisely each measurement is stored. Neither one is volume.
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What you need to know
- Explain sample rate and bit depth, and how each relates to quality.
- Tell uncompressed, lossless-compressed and lossy-compressed audio apart.
- Recommend a format using the product and how it will be delivered.
Start here
Recording is measuring, over and over
Sound is a continuously changing signal. A digital recording measures how strong it is at regular intervals, and each measurement is a sample. Sample rate is how many of those you take per second, in hertz or kilohertz. 44.1 kHz means 44,100 samples every second — it does not mean volume, and it does not mean bits.
A higher sample rate can represent higher-frequency detail, and it creates more samples to store for the same length of recording. What it cannot do is rescue a recording already made badly. If the microphone was poor, the room was noisy or the levels were wrong, the settings will not fix it afterwards.
How it works
Bit depth: how precise each measurement is
Bit depth is how many bits represent each sample. More bits mean more possible amplitude levels, so finer distinctions and less quantisation noise. It does not mean measurements are taken more often — that is sample rate, and confusing the two is the most common error here.
A 24-bit recording uses more bits per sample than a 16-bit one, which gives you more room to move when you are recording and editing. For the same duration and channels, more bits per sample means more data. The highest setting is not automatically the right one for a finished product.
| Setting | What it measures | Increasing it |
|---|---|---|
| Sample rate | Samples per second | More frequent measurements, higher-frequency detail, more data |
| Bit depth | Bits per sample | More precise amplitude levels, less quantisation noise, more data |
Try it
What each setting does — and does not do
Four settings across audio and video. The third column is the useful one: what people wrongly think each setting changes.
Learn the list
Working files and delivery files
Uncompressed means never reduced. Lossless compression makes it smaller and gives every bit back exactly. Lossy compression throws information away — usually information judged less noticeable — to get it smaller still. So a compressed file can absolutely preserve all its original data, as long as the compression was lossless.
And the extension is not a quality rating. WAV is commonly used with uncompressed PCM audio, but what is inside and at what settings is what matters. Neither WAV nor FLAC will repair a distorted source just by being saved as one.
| Example | What it does | When to reach for it |
|---|---|---|
| WAV with PCM audio | Uncompressed. | Preserves the recorded samples for editing. Files get large. |
| FLAC | Lossless compression. | Smaller, with the audio data recoverable exactly. Check the player supports it. |
| MP3 | Lossy compression. | Compact and supported everywhere — good for distributing speech or music. |
| AAC | Lossy compression. | Common delivery audio, including online, where the target player supports it. |
Two things that are not true
“A higher sample rate makes it louder” — no, it takes more measurements per second. “Lossy compression removes the background noise” — no, it removes audio information, and background noise is usually still there.
In the exam
Recording a local-history podcast
The same reasoning changes with the purpose. For a music archive where exact preservation is the point, lossless compression is the stronger choice — it is smaller than uncompressed but still recoverable bit for bit.
Worked answer
4 marks
A team records interviews for a local-history podcast, then publishes episodes for listeners to download on their phones. Explain the file format choices at each stage.
Tempting, but this does not score
They should record in MP3 because it is a small file that works on phones, and then upload the MP3 to their website for people to download.
Recording straight to MP3 means editing a file that has already had information discarded, and every re-save loses more. The working stage and the delivery stage need different answers.
Worth writing
Record and edit as uncompressed WAV with PCM audio, so the captured samples are preserved while they cut speech and balance levels — that avoids compressing the same audio repeatedly during production, at the cost of needing more storage. Then export the finished episode as MP3, because lossy compression brings the download size down for listeners on phones and mobile data, and MP3 plays on practically any player. Before publishing, listen back to the export to check the speech is still clear and quiet words have not been lost.
Where the marks come from
- Separates the working file from the delivery file, which is the point of the question.
- Explains why uncompressed matters during editing — no repeated compression.
- Names the trade-off honestly: more storage needed.
- Ties MP3 to the listeners described — phones and mobile data — and adds the check.
Key takeaways
- Sample rate = measurements per second. Bit depth = bits per measurement.
- Higher settings mean more data for the same length of recording.
- Neither setting repairs a noisy or distorted recording.
- Keep a good source for editing, then export a delivery copy that suits the platform.
- A file extension tells you nothing about how good the recording sounds.
Glossary
- Sample
- A measurement of a sound signal’s amplitude at one point in time.
- Sample rate
- How many audio samples are taken per second.
- Bit depth
- How many bits represent the amplitude of each sample.
- Quantisation noise
- Noise introduced by rounding each measurement to the nearest available level.
- Lossless audio
- Audio compressed so the original data comes back exactly.
- Master
- The retained high-quality version you produce delivery copies from.
Test yourself
6 questions
What does a sample rate of 48 kHz mean?
48,000 samples are taken every second.
Which setting increases the number of possible amplitude levels?
Bit depth — more bits per sample means finer amplitude measurements.
Why might MP3 suit a downloadable spoken guide?
Lossy compression cuts the file size, so it downloads faster and takes less space, while a sensible export setting keeps the speech clear.
Why keep an uncompressed or lossless source while editing?
It preserves the captured audio and avoids stacking up losses from re-encoding the same audio again and again.
Does a higher sample rate make a recording louder?
No. It takes more measurements per second. Loudness is not what either setting controls.
Can saving an MP3 as WAV restore what was lost?
No. The WAV stores the decoded audio, but information the MP3 discarded is gone for good.
Common questions
Are sample rate and bit depth the same thing?
No, and this is the distinction the exam tests. Sample rate is how often you measure. Bit depth is how precisely you store each measurement.
Should I always record at the highest settings available?
Higher settings give you more to work with and cost storage. Match them to the product — a spoken podcast does not need what a music master does.