That Blue Square Thing

Syllabus content:

Unit 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

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.

Sound Representation – everything you need to know

Sound Waves – slides from class

Sampling Rate and Resolution – slides from class

Sound 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:

Audio 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 speaker...