That Blue Square Thing

Syllabus content:
PDF iconUnit 3 audio content - just sound encoding
Note: this syllabus content is a slightly amended version of the one published freely on the web by AQA. I have made very minor adjustments to remove some content less suitable for students to use and it is presented here simply to allow the children I teach to download a usable copy of the syllabus content. It is copyright AQA and reproduced here simply to make access easier for students. No attempt to claim copyright is being made, although I could have copied the text into my own interpretation...

AQA Computer Science GCSE

This page is up to date for the new AQA 8525 syllabus for exams from 2022.

Data Representation - Representing Sound

Sound also needs to be turned into numbers to turn it into a digital sound file.

This is done by taking a sample on a regular basis across an analogue signal (a sound wave) and recording the amplitude (the volume). This can be expressed as a number - which ultimately becomes a binary value.

The more frequent the sample rate the better quality the audio is - and the large the file. Music files will tend to sample 44,100 times a second, which is a lot of data.

PDF iconSound Representation - everything you need to know

PDF iconSound Waves - slides from class

PDF iconSampling Rate and Resolution - slides from class

PDF iconSound File Size - a calculation based on a real 3 minute record

There's an audio file summary that I made for revision purposes as well:

PDF iconAudio summary

Analogue v Digital

The difference between a digital piano and an acoustic piano (one which creates a purely analogue sound) is that the sound from the acoustic piano resonates much more and the "fills a larger space". It's "bigger" and the bass sound in particular sustains more. It has a "richer" sound with more "depth", particularly depth of pitch (there is a bigger difference between the low notes and the high notes.

Of course, this is dependent on a quality of the piano. A really good quality (and generally more expensive) digital piano will sound much better - and better than a poorly maintained and/or cheap acoustic piano.

The same thing is probably true of hi-fi equipment. A cheap record player might well sound worse than a high quality CD player, despite the CD playing digital audio. Both will probably sound better than the music coming from your phone's speakers...