Year 10 WJEC Computer Science: Oral & Listening Exam Prep – Audio Input, Output and Sound Representation | WJEC Year 10 计算机：口语与听力备考专项

📚 Year 10 WJEC Computer Science: Oral & Listening Exam Prep – Audio Input, Output and Sound Representation | WJEC Year 10 计算机：口语与听力备考专项 – 音频输入输出与声音表示

When we talk about ‘speaking’ and ‘listening’ in Computer Science, we are not referring to human language exams but rather to how a computer system captures sound (hearing) and produces sound (speaking). This revision guide focuses on the Year 10 WJEC Computer Science topic of audio input/output devices, analog-to-digital conversion, sampling, bit depth, and sound file size calculations – core concepts that often appear in written assessments and are essential for understanding multimedia systems.

在计算机科学中，“口语”与“听力”并非指人类的语言考试，而是比喻计算机如何通过麦克风“听”到声音，又如何通过扬声器“说”出声音。本备考专项为 WJEC Year 10 计算机科学设计，深入讲解音频输入输出设备、模数转换、采样、位深度以及声音文件大小的计算。这些内容是笔试中常见的考点，也是理解多媒体系统的基础。

1. Speaking & Listening in Computing: Input and Output Devices | 计算机的“说”与“听”：输入输出设备

In a computer system, the ability to ‘hear’ is provided by input devices such as microphones, which convert sound waves into electrical signals. The ability to ‘speak’ is delivered by output devices like speakers or headphones, which convert electrical signals back into sound waves. These devices bridge the gap between analog audio and digital processing.

在计算机系统中，“听力”由麦克风等输入设备实现，它们将声波转换为电信号；“说话”则由扬声器或耳机等输出设备完成，它们将电信号重新转换为声波。这些设备在模拟音频与数字处理之间架起了桥梁。

Microphones are essential for voice recognition, recording, and communication applications. Speakers allow users to hear music, system alerts, and synthesized speech. Both are considered peripheral devices and are often connected via USB, 3.5mm jack, or wirelessly through Bluetooth.

麦克风是语音识别、录音和通信应用的关键设备，扬声器则让用户能够听到音乐、系统提示音和合成语音。两者都属于外围设备，通常通过 USB、3.5mm 音频接口或蓝牙无线连接。

2. How Sound is Captured: Microphones and Analog Signals | 声音如何被捕捉：麦克风与模拟信号

Sound travels as pressure waves in the air. A microphone contains a diaphragm that vibrates when these waves hit it. The movement is converted into a continuously varying electrical voltage – an analog signal. This signal closely mirrors the original sound wave’s amplitude and frequency, but it cannot be processed directly by a digital computer.

声音以气压波的形式在空气中传播。麦克风内部有一个振膜，当声波撞击时振膜随之振动。这种振动被转换为连续变化的电压信号——即模拟信号。该信号忠实地反映了原始声波的振幅和频率，但数字计算机无法直接处理它。

This is the first stage of the computer’s ‘listening’: capturing the richness of real-world sound in electrical form. The analog signal is then passed to a special component for digitisation.

这就是计算机“听力”的第一阶段：以电信号的形式捕捉真实世界丰富的声音。随后，这个模拟信号会被传送给一个特殊的组件进行数字化。

3. From Analog to Digital: The Role of ADC | 从模拟到数字：模数转换器的作用

To be stored and manipulated by a computer, the analog audio signal must be converted into binary data. This conversion is performed by an Analog-to-Digital Converter (ADC). The ADC samples the voltage at regular intervals and assigns each sample a binary number according to its amplitude.

为了能被计算机存储和处理，模拟音频信号必须转换为二进制数据。这一转换由模数转换器（ADC）完成。ADC 以固定的时间间隔对电压进行采样，并根据每个采样点的振幅分配一个二进制数值。

The quality of the resulting digital audio depends heavily on two factors: how frequently the ADC takes samples (sampling rate) and how many bits are used to store each sample (bit depth). Understanding these parameters is crucial for your WJEC exam.

最终数字音频的质量主要取决于两个因素：ADC 采样的频率（采样率）以及用于存储每个样本的比特数（位深度）。理解这些参数对 WJEC 考试至关重要。

4. Sampling: The ‘Listening’ Speed | 采样：计算机“听”的速度

The sampling rate, measured in Hertz (Hz) or kilohertz (kHz), determines how many times per second the ADC measures the amplitude of the analog signal. A higher sampling rate captures more detail of the original sound wave, leading to a more accurate representation but also a larger file size.

采样率以赫兹（Hz）或千赫兹（kHz）为单位，决定了 ADC 每秒测量模拟信号振幅的次数。更高的采样率能捕捉原始声波的更多细节，使声音表示更精确，但文件也会更大。

For CD-quality audio, the sampling rate is 44.1 kHz, meaning 44,100 samples are taken every second. The Nyquist theorem states that to accurately reconstruct a sound, the sampling rate must be at least twice the highest frequency you wish to capture. Human hearing ranges up to about 20 kHz, so 44.1 kHz is sufficient.

CD 音质的采样率为 44.1 kHz，即每秒采集 44,100 个样本。奈奎斯特定理指出，要精确还原声音，采样率必须至少是希望捕获的最高频率的两倍。人类听觉范围上限约为 20 kHz，因此 44.1 kHz 足够。

Common sampling rates you may encounter in WJEC questions:

Speech/telephone quality: 8 kHz
FM radio quality: 22.05 kHz
CD quality: 44.1 kHz
DVD/studio quality: 48 kHz or 96 kHz

WJEC 考题中常见的采样率：

语音/电话音质：8 kHz
调频广播音质：22.05 kHz
CD 音质：44.1 kHz
DVD/录音室音质：48 kHz 或 96 kHz

5. Bit Depth: How Precisely the Computer ‘Hears’ | 位深度：计算机“听力”的精细度

Bit depth refers to the number of bits used to represent each sample. A higher bit depth allows finer distinctions between amplitude levels, reducing quantization noise and improving dynamic range. For instance, a 16-bit depth provides 2¹⁶ (65,536) possible amplitude values, while 24-bit depth offers 2²⁴ (16,777,216) levels.

位深度指用于表示每个样本的比特数。位深度越高，振幅层级区分就越精细，这能减少量化噪声并扩大动态范围。例如，16 位深度提供 2¹⁶（65,536）种可能的振幅值，而 24 位深度则提供 2²⁴（16,777,216）种层级。

CD audio uses 16-bit depth, which is adequate for most listening environments. Professional audio recording often uses 24-bit to capture subtle nuances. In WJEC exams, you should be able to explain why a higher bit depth leads to more accurate sound reproduction but also larger file sizes.

CD 音频采用 16 位深度，适合大多数聆听环境。专业录音常采用 24 位以捕捉细微差别。在 WJEC 考试中，你需要能够解释为什么更高的位深度会使声音还原更准确，但同时会增大文件体积。

6. Calculating Audio File Sizes | 音频文件大小的计算

File size calculation is a key exam skill. The basic formula in bits is:

File Size (bits) = Sampling Rate (Hz) × Bit Depth × Duration (s) × Number of Channels

文件大小计算是一项关键的考试技能。基本公式（以比特为单位）如下：

文件大小 (比特) = 采样率 (Hz) × 位深度 × 时长 (秒) × 声道数

To convert to bytes, divide by 8. Further division by 1024 gives kilobytes (KB), and by 1024² gives megabytes (MB). Always show your working clearly.

转换为字节需除以 8；再除以 1024 得到千字节 (KB)，除以 1024² 得到兆字节 (MB)。解题时务必清晰展示每一步演算。

Example: Calculate the size in MB of a 30-second stereo CD-quality audio clip. (44.1 kHz, 16-bit)

Size (bits) = 44,100 × 16 × 30 × 2 = 42,336,000 bits

Size (bytes) = 42,336,000 / 8 = 5,292,000 bytes

Size (MB) = 5,292,000 / (1024×1024) ≈ 5.05 MB

示例：计算一个 30 秒立体声 CD 音质音频文件的大小（单位：MB），参数为 44.1 kHz、16 位。

大小 (比特) = 44,100 × 16 × 30 × 2 = 42,336,000 比特

大小 (字节) = 42,336,000 / 8 = 5,292,000 字节

大小 (MB) = 5,292,000 / (1024×1024) ≈ 5.05 MB

Remember to check if the question asks for an answer in KB, MB, or GiB and whether stereo (×2) or mono (×1) is specified.

答题时务必注意题目要求的结果单位是 KB、MB 还是 GiB，以及指定的是立体声（乘 2）还是单声道（乘 1）。

7. Speaking Back: Digital to Analog and Speakers | 计算机的“说”：数字到模拟转换与扬声器

When a computer ‘speaks’, it must reverse the digitisation process. The stored binary audio data is fed into a Digital-to-Analog Converter (DAC). The DAC reconstructs the analog electrical signal from the binary samples, essentially ‘connecting the dots’ to recreate a smooth waveform.

当计算机要“说话”时，必须逆转数字化流程。存储的二进制音频数据被送入数模转换器（DAC）。DAC 根据二进制样本重建模拟电信号，过程类似于“连点成线”，重新生成平滑的波形。

This analog signal is then amplified and sent to a speaker. The speaker’s electromagnet and cone vibrate, pushing air and creating sound waves that our ears perceive. The entire chain – microphone → ADC → storage → DAC → speaker – is the full loop of computer ‘hearing’ and ‘speaking’.

重建后的模拟信号经过放大后驱动扬声器。扬声器中的电磁铁与振膜振动，推动空气产生我们耳朵能感知的声波。整个链路——麦克风 → ADC → 存储 → DAC → 扬声器——就是计算机“听力”与“口语”的完整闭环。

8. Sound Quality and Compression | 音质与压缩

The relationship between sampling rate, bit depth, and file size presents a trade-off. High-resolution audio offers superior quality but consumes significant storage and bandwidth. Compression techniques are used to reduce file size. In WJEC, you should know the difference between lossy and lossless compression for audio.

采样率、位深度与文件大小之间存在取舍关系。高解析度音频质量优越，但会消耗大量存储空间和带宽。压缩技术被用来缩减文件体积。在 WJEC 考试中，你需要了解音频的有损压缩与无损压缩之间的区别。

Lossy compression (e.g., MP3, AAC) permanently removes some audio data deemed inaudible by psychoacoustic models. This greatly reduces file size with minimal perceived quality loss. Lossless compression (e.g., FLAC, ALAC) preserves all original data while still reducing size, much like ZIP for audio.

有损压缩（如 MP3、AAC）会根据心理声学模型永久性地移除一些人耳不易察觉的音频数据，从而大幅减小文件体积，而听感质量损失极小。无损压缩（如 FLAC、ALAC）则保留全部原始数据，同时仍能缩减体积，类似于音频专用的 ZIP。

Compression Type	Examples	Data Removed?	Quality
Lossy	MP3, AAC, OGG	Yes	Good to very good, but irreversible
Lossless	FLAC, ALAC, WAV (uncompressed)	No	Identical to original

Table comparing lossy and lossless audio compression

有损与无损音频压缩对比表

9. WJEC Exam-Style Practice: Listening and Speaking Scenarios | WJEC 考试风格练习：听力与口语场景

The following practice questions mirror typical WJEC written tasks that test your understanding of audio capture and playback. For each one, outline the key points you would include in your answer.

以下练习题模仿了典型的 WJEC 笔试题型，用于检测你对音频捕捉与回放的理解。针对每一题，列出你作答时需要涵盖的关键点。

Q1. A student records a 10-second Mono voice note on a smartphone. The recording uses a sampling rate of 8 kHz and a bit depth of 8 bits. Calculate the file size in kilobytes. Explain why this combination is suitable for voice but not for music.

Q1. 一名学生在智能手机上录制了一段 10 秒的单声道语音便签。录音采用 8 kHz 采样率和 8 位位深度。请以千字节为单位计算文件大小，并解释为何该参数组合适合语音却不宜用于音乐。

Sample answer: Size = 8000 × 8 × 10 × 1 = 640,000 bits; 640,000 / 8 = 80,000 bytes; 80,000 / 1024 ≈ 78.13 KB. 8 kHz captures frequencies up to 4 kHz, enough for speech but not for higher musical frequencies; 8-bit depth limits dynamic range, causing noticeable noise on music.

参考答案：大小 = 8000 × 8 × 10 × 1 = 640,000 比特；640,000 / 8 = 80,000 字节；80,000 / 1024 ≈ 78.13 KB。8 kHz 只能捕捉 4 kHz 以下的频率，对语音足够但远低于音乐所需；8 位位深度限制动态范围，用在音乐上噪声明显。

Q2. Describe the role of the ADC and DAC in a video conferencing application. How does increasing the sampling rate affect the user’s experience?

Q2. 描述视频会议应用中 ADC 和 DAC 的作用。提高采样率会如何影响用户体验？

Key points: ADC converts the speaker’s voice (analog) into digital data for transmission; DAC at the receiver converts digital back to analog for the listener. Higher sampling rate captures more detail, making voices sound clearer but requires more network bandwidth.

要点：ADC 将发言者的模拟语音转换为数字数据以便传输；接收端的 DAC 将数字信号转回模拟信号供收听者聆听。更高的采样率可捕捉更多细节，令语音更清晰，但会占用更多网络带宽。

10. Top Tips for the ‘Oral & Listening’ Topic in Your Revision | 备考“口语与听力”专题的最佳技巧

Treat this topic as a story of two conversions: analog capture (listening) and analog playback (speaking). Master the key terms: microphone, ADC, sampling rate, bit depth, DAC, speaker, sample. Be ready to calculate audio file sizes confidently. Use mnemonics like ‘Sample Rate x Bit Depth x Time x Channels’ – remember S×B×T×C.

把这部分内容当作两端转换的故事来看：模拟捕捉（听）与模拟回放（说）。熟练掌握关键术语：麦克风、ADC、采样率、位深度、DAC、扬声器、样本。要能自信地计算音频文件大小。记住公式缩写 ‘S×B×T×C’（采样率 × 位深度 × 时长 × 声道）。

Always write out the formula first, then substitute values, and perform conversions step by step.
率先写出公式，再代入数值，然后逐步进行单位换算。
Practise explaining the trade-off between quality and file size in everyday scenarios, such as streaming versus downloading high-fidelity audio.
练习在日常场景中解释音质与文件大小的权衡，例如流媒体播放与下载高保真音频的区别。
Review the differences between lossy and lossless compression with examples, as this often appears in multiple-choice or short-answer questions.
复习有损与无损压缩的区别及实例，这部分常出现在选择题或简答题中。
When a question mentions ‘improving the listening experience’, think immediately of increasing both sampling rate and bit depth, but also note the side effect on storage.
当题目提到“提升聆听体验”时，要立刻想到提高采样率和位深度，同时也要指出这对存储的影响。

Published by TutorHao | Computer Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Year 10 WJEC Computer Science: Oral & Listening Exam Prep – Audio Input, Output and Sound Representation | WJEC Year 10 计算机：口语与听力备考专项 – 音频输入输出与声音表示