Task summaryWhat you will learn:
How to estimate the download time of a file. Understand that a sound file can be represented as a graph. How you will be assessed: A short written assessment. |
Key terminologySample Rate:
The number of samples recorded per second measured in hertz (Hz). |
Activities
Sampling Sound
Sounds are recorded by taking a sample of the sound at regular intervals. This value is then stored as a binary number. A higher sample rate provides more samples which gives a more detailed and accurate recording of the sound.
Once each sample has been recorded the computer plots it on a graph and then fills in the line between each sample to produce the waveform that you can see using a sound-editing program. Having more samples, or more points on the graph, makes it much easier to fill in those lines accurately.
When a sound is played, the computer sends each signal to a speaker to recreate the sound. A sound file with more samples will be more accurate than a sound file with fewer samples. Of course more samples means that more bits are needed to store the data, so more samples mans a bigger file size. A standard CD recording will be recorded at 44.1 kHz, using this sample rate it is difficult to distinguish between a recording and the real thing. The memory required to store 1 minute of music at this sample rate would be calculated as, assuming the file was a 16 bit file:
- 1 kHz = 1000 samples per second
- 44.1 kHz = 44100 samples per second
- 16 bits per sample x 44100 samples per second = 705,600 bits per second.
- 705,600 bits per second / 8 = 88,200 bytes per second x 60 seconds = 5,292,000 Bytes or 5.292 MB per minute.
Listen to the following: Can you identify the song when every 3rd note is missing? Play Song.
Complete the following worksheet about waveforms.
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Watch the two videos on the left. The first explains how digital audio works and the second video demonstrates how to use the knowledge obtained by learning about digital sound.
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Channels - Most music playback systems use a two-channel system, this is called stereo. Stereo has a left channel and a right channel. Each channel requires data, so on a stereo system twice as much data is stored. Many homes now have surround sound systems, these use more than two channels and therefore would require data for each channel. Common surround sound systems can vary between 5.1 and 7.1 channels.
Assessment Task
- Download these two files. Sample 1 and Sample 2 using Audacity on the PC open each of the files and listen to the tracks. Why do you think Sample 1 sounds so terrible compared to Sample 2 - you can answer on the assessment?
- Complete this assessment on sampling.