That Blue Square Thing

AQA Computer Science GCSE

July 2019: the AQA CompSci area is almost complete. Most of the content for units 3-6 is now up and there's quite a lot of Unit 7 material. There's still some work to do, particularly on Paper 1 units, but it's getting there.

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 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

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...