Stretch tasks Storing Sound

Round 1: Quiz Blitz

1. Measuring a sound wave's amplitude at regular intervals Each measurement is rounded and stored in binary, giving a list of numbers that approximates the wave.
2. The number of samples taken each second Sample rate is how often you measure, in hertz.
3. The number of bits stored for each sample Bit depth is how precisely each measurement is recorded.
4. False Samples are taken at intervals and rounded to fixed levels, so it is always an approximation.
5. 180 3 x 60 = 180. Always convert minutes to seconds before a sound calculation.
6. Hertz Hertz means per second: 44,100 Hz is 44,100 samples every second.
7. A higher sample rate; A higher bit depth File size is sample rate x duration x bit depth, so raising either one grows the file.
8. 256 2 to the power 8 is 256 levels.
9. Doubles it Stereo has two channels, so there is twice as much data.
10. A microphone turns the sound into an electrical signal → An analogue to digital converter measures the signal → Each measurement is rounded to the nearest level → The value is stored in binary Microphone, converter, rounding, then binary.
11. False It makes the recording more accurate, not louder.
12. Bit depth Sample rate is how often. Bit depth is how precisely.

Round 2: Quick Fire

1. • Sample rate is the number of samples taken per second
   • Bit depth is the number of bits used to store each sample
   Model answer

   Sample rate is the number of samples taken per second. Bit depth is the number of bits used to store each sample.

2. • Samples are taken more often, closer together
   • So the digital version follows the original wave more accurately
   Model answer

   More samples are taken each second, so they are closer together and the digital version follows the shape of the original wave more accurately.

3. • A microphone turns the sound into an electrical signal
   • The amplitude is measured at regular intervals
   • Each measurement is rounded and stored in binary
   • By an analogue to digital converter
   Model answer

   A microphone turns the sound into an electrical signal. An analogue to digital converter measures its amplitude at regular intervals, and each measurement is rounded to the nearest level and stored in binary.

4. • Each sample is less precise, so quality falls
   • A smaller file
   Model answer

   Each sample is stored less precisely, with fewer levels, so the quality is lower. The file is smaller.

Round 3: Big Think

1. • 3 x 60 = 180 seconds
   • 44,100 x 180 x 16 = 127,008,000 bits
   • Divide by 8: 15,876,000 bytes
   • Divide by 1000 twice: 15.876 MB
   Model answer

   3 x 60 = 180 seconds. 44,100 x 180 x 16 = 127,008,000 bits. 127,008,000 / 8 = 15,876,000 bytes. 15,876,000 / 1000 = 15,876 KB, and 15,876 / 1000 = 15.876 MB.

2. • Low sample rate: fewer samples per second, further apart
   • So the wave's shape is followed roughly, losing higher frequencies
   • Low bit depth: fewer levels, so each amplitude is less precise
   • So quiet details are lost
   • Raising both makes the recording more accurate, with better quality
   • But the file becomes larger, in proportion
   • Digital sound is only ever an approximation of the analogue wave
   Model answer

   A low sample rate means fewer samples per second, so the samples are further apart and the digital version follows the shape of the original wave only roughly: higher frequencies are lost and it sounds duller. A low bit depth means fewer levels for each measurement, so every amplitude is rounded less precisely and quiet details are lost. Digital sound is always an approximation of the analogue wave. If both settings were increased, the recording would be more accurate and closer to the original, giving better quality, but the file would be larger, because the size grows in proportion to the sample rate and the bit depth.

This or That

1. 44,100 samples every second Hertz is per second, so that is 44,100 measurements each second.
2. A higher bit depth More bits per sample give more levels, so small changes in amplitude survive.
3. Time Sample rate is how often you measure. Bit depth works up the amplitude axis.
4. A sound wave in the air A real sound wave varies continuously. An MP3 is a list of binary numbers.
5. Turn it into seconds Sample rate is per second, so the duration must be in seconds too.
6. 65,536 2 to the power 16 is 65,536.
7. Measures the signal and outputs binary It samples the electrical signal from the microphone and outputs binary values.
8. Doubles it File size grows in proportion to the sample rate.

Memory Match

• A 3 Sampling: Measuring a wave at regular intervals
• B 4 Sample rate: Measurements taken each second, in hertz
• C 6 Bit depth: Bits stored for each measurement
• D 2 Amplitude: The height of the wave: its loudness
• E 1 Analogue: Continuously varying, like real sound
• F 5 Stereo: Two channels, so twice the data

Sort It

1. Sample rate Measured in hertz Hertz means per second: sample rate counts samples each second.
2. Sample rate How many samples are taken each second That is the definition of sample rate.
3. Bit depth Raising it keeps quiet details Small changes in amplitude are no longer rounded away.
4. Sample rate Works along the time axis Sample rate is about how often you measure.
5. Bit depth Raising it records each measurement more precisely More bits give more levels to round each sample to.
6. Bit depth 16 of these give 65,536 levels 16 bits per sample give 2 to the power 16 levels.
7. Bit depth Works along the amplitude axis Bit depth is about how precisely each height is recorded.
8. Sample rate Raising it captures higher frequencies Samples closer together can follow faster changes in the wave.
9. Bit depth How many bits store each sample That is the definition of bit depth.
10. Sample rate CD quality uses 44,100 of these CDs take 44,100 samples every second.