Representing sound in binary - Answers
Q1. A microphone is an input device.
Q2. Speakers are an output device.
Q3. A microphone is connected to the sound card.
Q4. An analogue signal is one that constantly changes, that has an infinite number of possible values and is characterised by a waving line on a graph.
Q5. A digital signal is one where the reading has fixed, defined intervals. E.g. If you have one bit, there are only 2 possible readings: 0 and 1. If you have 2 bits, you can only have (in decimal) 0, 1, 2 and 3.
Q6. Three file formats for digital songs, apart from MP3: WAV, ogg, au, ra - there are lots!
Q7. The sample interval is the time taken between samples.
Q8. The sample rate is how many samples you take in a fixed amount of time e.g. a second.
Q9. The sample rate tells you how many readings to take in a second. If you divide 1 by (sample rate - 1), you get the sample interval. e.g. If the sample rate = 5, the sample interval = 1 / (5 - 1) = 0.25s so there is an interval of 0.25s between readings.
Q10. Ripping a music CD means converting digital files on a CD (which are usually in a digital format that can't be read by MP3 players and phones) into a format that can be read by MP3 players, phones etc.
Q11. Explain how music is streamed: Streamed music is where you listen to the music as it is downloaded from the Internet as opposed to downloading and saving the whole song first and then playing it. As the first few seconds of a streamed song is downloaded, it is put into a special storage area called a 'buffer' and then playing starts. While that part of the song is played, more of the song is being downloaded and buffered. If the files are too large, however, then you can't download it quickly enough for it to be buffered and played. The song stops for a little while, to give your computer the time to download more of the song before playing can resume.
Q12. Raw sound files are converted into MP3 files because they are large. Converting them makes the file smaller, although you lose a bit of quality (which most people can't tell).
Q13. Two raw, uncompressed sound file formats: RAW, WAV and AIFF.
Q14. Two sound codecs: MP3, ogg.
Extension work
It would be useful for students to be given some time and direction to experiment with some of the things they have learnt about digitalising sound. There are lots of open source software for ripping CDs. Below are some ideas for practical tasks that could be done in school or perhaps set for homework.
Practical work: Experiment with some software for ripping a music CD. you can find lots of applications by searching for e.g. 'best free software for ripping a CD'. Find the settings for quality and adjust the sample rate. Record the same song at the lowest quality and the highest quality. Can you hear the difference when you play the songs back? Compare the file sizes of the same songs recorded at different qualities. How different are they? Do different software applications recording at the same quality produce results that are the same? Experiment!