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IDC4O - Audio
Sound
Sound is vibrations that we can hear. These vibrations travel as a wave through the air very quickly (20 to 20,000 vibrations per second). The speed of these vibrations will determine the pitch (high or low).
Analog Recording
Everything that we see and hear is analog. An analog cassette will "draw" the soundwave onto magnetic tape in the same shape that is detected by the microphone. When it is played back, the fluctuations of the soundwave on the cassette will cause the amplifier to fluctuate a speaker with the same vibrations.
Digital Recording
The modern recording industry relies on digital technology because it has a lot of advantages. However, it is not possible to get rid of analog technology entirely. Everything we hear is analog. It is not possible to listen to digital music. It can be stored digitally, but it must then be converted to an analog signal for us to hear it. A microphone is an analog device, and the only way we can record digital music is to convert the analog signal into a digital one.
Why digital?
Analog recording mediums degrade over time and the sound wave gradually gets distorted with use. If that signal is converted to a series of numbers and stored on a hard-drive, then that information can be retrieved many more times without distortion, and it can be easily duplicated for backup. But that is not the most impressive advantage of digital recording. It is very difficult to edit an analog recording, and even then it has many limitations. But the numbers that are stored on a digital recording can easily be manipulated on a computer. This allows us to easily modify the sound wave in a recording.
ADC - analog to digital converter transforms an analog sound wave on a microphone into a series of numbers that are stored on a computer
DAC - digital to analog converter transforms the numbers back into an analog signal that we can be amplified into speakers
* the analog signal produced by the DAC is never 100% accurate to the original analog signal - this is why some people prefer analog recording, because there is no loss of signal due to conversion.
Why digital?
Analog recording mediums degrade over time and the sound wave gradually gets distorted with use. If that signal is converted to a series of numbers and stored on a hard-drive, then that information can be retrieved many more times without distortion, and it can be easily duplicated for backup. But that is not the most impressive advantage of digital recording. It is very difficult to edit an analog recording, and even then it has many limitations. But the numbers that are stored on a digital recording can easily be manipulated on a computer. This allows us to easily modify the sound wave in a recording.
ADC - analog to digital converter transforms an analog sound wave on a microphone into a series of numbers that are stored on a computer
DAC - digital to analog converter transforms the numbers back into an analog signal that we can be amplified into speakers
* the analog signal produced by the DAC is never 100% accurate to the original analog signal - this is why some people prefer analog recording, because there is no loss of signal due to conversion.
We can do two things to improve the picture quality of a video:
Likewise, we can do two things to improve the sound quality of a digital recording:
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Copyright
Generally, it is illegal to copy music unless it is public-domain and royalty-free. Otherwise, even if you are not selling the music, you must purchase it for your own enjoyment. It is expected that any audio that you obtain for this course is something that you have recorded yourself, or is obtained legally.
Mono Sound
Mono recording is the simplest recording type - a single layer that is played back through one or more speakers. Even if the recording is played back through two speakers, it cannot be stereo because there is only one recorded source.
Multitracking
Multitracking is the concept of recording individual parts as separate layers which can be played simultaneously but edited individually. They are later combined into one single audio layer called the "mix".
For instance, a rock band may record a song using individual tracks for each musician. If a single musician makes a mistake, the whole band will not have to record the song over. Instead, the musician that made the mistake will record over the part that needs to be corrected. In the example shown on the left, there are 6 layers of stereo tracks which are explained below... |
Stereo Sound
Stereo sound requires 2 separate speakers with 2 separate sound sources to produce a multidimensional effect. Much like a 3D movie requires 2 eyes that see 2 similar (but different) viewpoints, true stereo sound cannot be achieved with a single speaker, and even if there are two speakers, the speakers must have two different sound sources.
For example, the stereo track below has a recording for the left speaker, and a separate recording for the right speaker. Notice that the Left speaker starts off quiet and gradually gets louder. The right speaker starts off loudly and gradually gets quieter. When they are played together, the ears will detect motion.
For example, the stereo track below has a recording for the left speaker, and a separate recording for the right speaker. Notice that the Left speaker starts off quiet and gradually gets louder. The right speaker starts off loudly and gradually gets quieter. When they are played together, the ears will detect motion.
Surround Sound
Surround sound is a complex technology that extends far beyond a standard 2 source system. Though we only have two ears, the brain takes in many factors that are decoded to determine the exact location of a sound. For a detailed understanding of the theory and technology, read this article.
Microsoft Sound Recorder (Voice Recorder)
The app installed with Microsoft Windows allows you to make a simple recording through the microphone. There are no significant editing features available on it, but it will save into a file that can be dropped into better software.
Exercise: Make a recording of a simple sentence. Speak slowly so that you will be able to visually identify the individual words. |
Music Lab
The Music Lab online tool allows you to generate audio files by dragging in layers of instruments.
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Audacity
Audacity is an excellent audio package that is a free download. There is no expectation that students download the software at home. As with all software, downloading is done at your own risk and is your own responsibility. At present, we are waiting on the technician to install the software on the laptops in the classroom.
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Online Audio Tools
Audio Tool Set is a free audio editor that does some of the things that Audacity is capable of. It will do as a temporary alternative to Audacity.
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Exercise 1:
Using a stereo track that has been recorded, select one side to fade in and select the other side to fade out.
Exercise 2:
Silence any areas within your recording that have slight/unwanted background noise.
Exercise 3:
Select individual words within a sentence and re-arrange the order of words to make it say something different.
Using a stereo track that has been recorded, select one side to fade in and select the other side to fade out.
Exercise 2:
Silence any areas within your recording that have slight/unwanted background noise.
Exercise 3:
Select individual words within a sentence and re-arrange the order of words to make it say something different.