An audio recording of a telephone keypad output when placing a seven-digit phone

Question

An audio recording of a telephone keypad output when placing a seven-digit phone call was recorded. A screen shot of the sound file information is shown in Figure 1. From the sound file information, determine:

a) Length of the recording (s)?

b) Number of audio channels recorded (e.g. stereo = 2 channels, mono = 1 channel)?

c) The sampling rate (Hz)?

d) The time step between samples (ms)?

e) Estimated number of data points you expect in the file?

128 KB Modified: Today, 12:53 PM Add Tags... ? General: Kind: Apple MPEG-4 audio Size: 128,094 bytes (131 KB on disk) Where: Macintosh HD Users johnhaglund Desktop Created: Today, 12:53 PM Modified: Today, 12:53 PM Stationery pad Locked More Info: Sample rate: 44,100 Duration: 00:07 Audio channels:2 ? Name & Extension:

Explanation / Answer

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a. Length of the recording = duration = 00:07 = 7 seconds (Mentioned on screen)

b. Number of audio channels = 2 (Mentioned on screen)

c. Sampling rate = 44,100 Hz (Mentioned on screen)

d. Time step between samples = 1/44100 = 0.022 milli seconds

e. Estimated number of data points = (duration/time step) x no of channels = (7/0.022m) x 2 = 617400

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