This is an extra bit that is 1 if the original binary data has an odd Then what? We can detect errors by transmitting someĪdditional, redundant information. Suppose we have a really bad bit of static, so a 1 turns into a 0 or The actual implementation of digital transmission is somewhat moreĬomplex than this, but the general technique is the same: two signals thatĪre easily distinguishable even when they are degraded. TheĬomputer files are (very probably) perfect copies of the original with a copy of a copy of a copy of a computer file. This restoration isn't possible with analog signals, because withĪnalog there aren't just two possibilities. Which are the 0s and which are the 1s, and restore it to: Thus, the previous signal might be degraded to theĭespite the general erosion of the signal, we can still figure out However, and this is the really cool part, theĭegraded signal can be "cleaned up," because we know that each bit isĮither 0 or 1. The signals used to transmit bits degrade, too, because any physical Indicate a 1 and falls to the minimum to indicate a 0.ĭegradation and Restoration of Digital Signals The heavy black line is the signal, which rises to the maximum to We first decide that, say, "high" means a 1 and "low" means a Suppose we want to transmit the number 6. Numbers, which we convert into bits and then transmit theĪ digital signal uses some physical property, such as voltage, With a digital signal, we are using an analog signal to transmit old televisions (intensity and color information per scanĪnalog technology always suffers from degradation when copied.Voltage, in proportion to the information that we are trying to The pictures we saw above are examples of analog signals:Īn analog signal varies some physical property, such as There doesn't have to be much degradation for it to have a noticeable Lessening of strength and there is some noise added near the second The degradation may not be immediately obvious, but there is a general Property of the signal, such as electrical voltage, pressure of a sound "telephone." Or think about photocopies of photocopies ofĪnd this is the received signal (dashed) compared to the transmitted When we continue to transmit and transform signals, theĮffect is compounded. signals may get combined with interference from other.signals may fade with time and distance.Stored on videotape or DVD and played on your home VCR or DVD player.Īny time signals are transmitted, there will be some Converted to laser light, then electricity whenĪ similar kind of story can be told about visual images.Converted to spots on a CD when the CD is.Converted to magnetism when it's put on a master tape.Converted to electrical signals by a microphone.Sound is simply pressure waves in air, caused by.Amplitude is measured in deciBels (we will see later that it Humans can hear frequencies between 20 Hz and 20,000 Frequency is measured in Hz orĬycles per second. Important characteristics are Frequency (aka pitch) andĪmplitude (aka loudness). Sound moves fast: in air, at 340 m/sec = 750 miles per hour. When sound is transmitted or stored it may need toĬhange form, hopefully without being destroyed.
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