dcf.cymru stimulus sheet · Music · Year 9
One recording, three ways to store and share it. The school, the concert and the storage limits are invented for this lesson. The facts about sound files are real.
Ysgol Gyfun Pen y Garnedd recorded its summer concert in July 2026 on a portable recorder. Mrs Rowlands, the Head of Music, wants every family to be able to hear it, and she wants a top-quality copy kept safely for the school archive. She has asked Year 9 to work out how big the files will be and how to store and share them.
| No. | Piece and performers | Length |
|---|---|---|
| 1 | Fanfare for a summer evening, brass ensemble | 1 min 40 s |
| 2 | Ar Lan y Môr (traditional), Year 7 choir | 3 min 10 s |
| 3 | Golau’r Haf (pupils’ own song), Year 10 rock band | 4 min 5 s |
| 4 | Calon Lân (traditional hymn), senior choir | 3 min 30 s |
| 5 | Blues in F, jazz band | 4 min 20 s |
| 6 | Summer medley, ukulele group | 2 min 45 s |
| 7 | Keyboard duet, 2 Year 8 pupils | 2 min 20 s |
| 8 | Guitar ensemble | 3 min 25 s |
| 9 | Year 9 samba band | 5 min 15 s |
| 10 | Twmpath dance set, folk group | 4 min 40 s |
| 11 | Harp solo, Year 10 pupil | 2 min 50 s |
| 12 | Wind band | 4 min 0 s |
| 13 | Musical theatre medley, drama club | 5 min 30 s |
| 14 | Finale, all performers | 5 min 0 s |
Uncompressed audio (WAV files) stores every sample. A sample is one measurement of the sound wave; the bit depth is how many bits each sample uses; stereo has 2 channels (left and right), mono has 1.
Size in bits = sample rate × bit depth × channels × seconds
Size in bytes = size in bits ÷ 8 (8 bits = 1 byte)
CD quality is 44,100 samples per second, 16-bit, stereo: 44,100 × 16 × 2 = 1,411,200 bits per second, which is 1,411,200 ÷ 8 = 176,400 bytes per second.
The school’s recorder can also record at 48,000 samples per second, 24-bit, stereo. That is the setting it used on the night.
MP3 files are compressed: the encoder throws away detail that most listeners will not notice. This is lossy compression, so the detail can never be put back. A WAV file is lossless. An MP3’s size depends on its bitrate, in kbps (kilobits per second). In this lesson 1 kbps = 1,000 bits per second.
MP3 size in bytes = bitrate in bits per second × seconds ÷ 8
320 kbps is the highest standard MP3 bitrate. 128 kbps is much smaller, and the loss of detail is easier to hear.
| Unit | Bytes |
|---|---|
| 1 kilobyte (kB) | 1,000 = 103 |
| 1 megabyte (MB) | 1,000,000 = 106 |
| 1 gigabyte (GB) | 1,000,000,000 = 109, which is 1,000 MB |
Computers sometimes count in 1,024s instead (1,024 bytes, then 1,024 × 1,024 bytes, and so on), so a file can look slightly smaller on screen. Real files are also a little bigger than the formula gives, because they store the title and other details. Ignore both today.
| Option | The facts |
|---|---|
| A. Email attachments | The school email system allows 20 MB of attachments in one email. 214 families would each need every email. |
| B. Shared folder on the school’s online drive | The music department has 500 MB of space left. Staff can send families a link set to view only, which can be switched off later. |
| C. USB memory stick | The department owns a 4 GB stick, kept in the locked music office. |
| D. Staff archive drive | A drive on the school network that only staff can open. It has plenty of space. Families cannot reach it. |
| E. A public video website | A parent has offered to upload the whole concert for anyone in the world to watch. |