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Intro to Digital Audio
About Audio
Digital Audio and video are pretty similar things. Capturing (digitizing), editing, timelines, codecs are the same principles. Audio does take up less room than video and requires less PC power as well. Video is more powerful as a communication device, and therefore gets a little more press.
Best intros I know... www.mediacollege.com/audio/01/index.html & Digital Audio Primer from www.adobe.com/motion/primers.html
Some other nice links are:
- www.indiana.edu/%7Eemusic/etext/digital_audio/chapter5_digital.shtml
- www.teamcombooks.com/mp3handbook/11.htm
- audacity.sourceforge.net/manual-1.2/index.html
Understanding Sound
There are a few things that you need to know about sound to understand how it works. First, sound is created by vibrations that move air molocules, forcing these molocules together to create a higher pressure, and travel like this in waves.
Links
dev.physicslab.org - WavesSound_IntroSound.xml
www.mediacollege.com/audio/01/sound-waves.html
www.mediacollege.com/audio/01/wave-properties.html
The 4 main parts of (analog) sound
- Wavelength - how long between two points with the same degree of phase
- Amplitude - reflects the change in pressure from the peak of the waveform to the trough. How high/low the waveform is.
- Cycle or Period - the amount of time it takes for a waveform to go from applitude peak to peak... .
- Frequency - the number of cycles per second, 1,000 Hz = 1,000 cycles per second.
Links
www.school-for-champions.com/science/sound.htm
library.thinkquest.org/19537/Physics3.html
How sound waves Interact
When different waves collide (e.g. sound from different sources) they interfere with each other. This is called, unsurprisingly, wave interference. When waveforms are in phase with each other they add together, when 180 degree out of phase they cancel each other out, otherwise they create new complex wave patterns.
Digital Sound
Dgital sound works in a different way because, well, it is digital. All microphones capture audio in an analog way... by coverting pressure waves into voltage. In analog media (like tapes) these voltage changes were transfered to tape as magnetic changes. With digital sound, they have to be digitized or sampled.
3 Main digital processes that affect quality
- Sampling Rate (frequency resolution) - How often a sample of sound is turned into numbers. The higher the rate, the closer the digital sample can match the shape of the original analog curve. To be a decent sample, the rate must be at least twice the speed of the frequency of the sound.
- Bit Depth (amplitude resolution) - How much storage will be used for each sample. 1 bit can only keep track of the sound being on or off... while 32 bit can do much, much more.
- Compression (lossless/lossy) - also a function of the format and codec used - Once a sound is sampled, it must be saved to the computer. Usually, the uncompressed sound (like a .WAV) is really large, so it is compressed with a codec. The compression can be either lossless (not losing any quality) or lossy (losing quality). Almost all are lossy.
Categories of Audio
First off... when you need to use audio for a project, there are a few different catagories of audio you can deal with:
- Music - all different types
- Voice-overs - just voice alone. Usually added with music
- Sound Effects - doors shutting, bangs, pops... etc. Often cheeeeeeeezy!
- Loops - short snippets of music that you loop together with ACID or Garage Band
- MIDI - Musical Instrument Digital Interface - original music form on the computer
Music
I guess you know what music is... so I'll go on.
Voiceovers
Everyone has heard a voice-over before... whether it's cheezy radio commercials, books on tape, corporate videos, or the commercial for the latest Hollywood movie with the guy that has that really low and spooky voice. Voice-overs can be down as stand-alone audio, or combined with music, other voices, or even animated characters. Fun to do, but
Sound Effects
One tricky type of audio to use is sound effects. They can be encredible, and can add lots of ambiance, or depth to your projects.... or they can ruin them altogether! So many sound effects are cheeezzzzy. To take some for a test drive, check out the site: www.simplythebest.net/sounds/ On these sites you will find some sound effects... but also real music too.
Looping Music
Another type of music you may need is loops. Loop music creation is one of the newer trends in audio production. It started years ago, but become popular with the introduction of ACID a number of years back. Loop music sometimes has a distinctive sound, but after playing with the software, you can see how easy it is to generate pretty cool, complex and fun soundtracks.
One of the main reasons to use looping music.. is that it is created by you, and so you have the ability to use that music on videos or projects that you make available to the world. Even youtube has caught onto this and posted a video about "How To Make Free and Legal Soundtracks For YouTube Videos." What is SOOOO COOL is that the music is created on the www.splicemusic.com website.. you don't even have to download software!!!Midi Audio
Last audio type you should know about use are MIDI files. The original audio format for the the computer (and the web). It's days are numbered. It's mathematical music in a way... and results in very small files. All you need to know is the what note it is, the length of the note, and the digital instrument to play it with, and there you have music. Some MIDI files are really amazing... but most on websites are really bad, and sound very dated. So... use at your own risk. They have many sites on the internet for midi files, but you can find some at www.simplythebest.net/sounds/ too.
Getting Audio onto your pc
Once you have the need for audio, you have the need for getting it on your pc. There are a few ways...
- Downloading
- Capturing (sampling/digitizing) from a source like a tape
- Converting from a cdrom (ripping) Note: A lot of people know how to stick a cd in their pc and use either iTunes or Windows Media Player to "rip" music off a cdrom and onto their pc (often into the "My Music" folder). Important thing to know for Microsoft users is that the default .wma file format is NOT compatible with most audio/video editors. The sound must usually be in WAV, AIFF, or MP3 formats to be used in various applications. You CAN set WMP to rip to the .mp3 format.
Downloading music
You may also download music from lots of different sites. There is only one that I know of where you can get really top notch royalty-free music for soundtracks for FREE. www.freeplaymusic.com Important thing about this site is that they have music available in all sorts of genres, and lengths. You can download a version of the same song from 10secs (for quick commercials) up to ~2mins (as soundtracks). This is a very common thing for professional music.
Another nice site for music is... www.newgrounds.com/audio and even better... www.megatune.com... creative commons music.
Sampling/Digitizing
A somewhat inexpensive pc microphone can do a decent job sometimes, but for really good quality, you have to have really good equipment. A really good mic can cost hundreds! If you recorded the voice to tape, you will need to play the tape (or DAT) and have the signal go into your sound card. Then use softwaree like Audacity or even Premiere to record the audio. Once you have it one the pc, you can edit to your heart's content.
Ripping Audio
Be careful with this. Make sure you have rights to use the files, even though for PURELY educational projects you are protected somewhat under the "fair Use" policy. To Rip music off your cdrom to WAV or MP3, use Windows Media Player or iTunes, or try a utility such as www.audiograbber.com-us.net/ or www.mgshareware.com/frmmain.shtml or... one of the other 1000+ rippers out there.
Compressing Audio
Just like video is compressed so that it doesn't take up as much room, audio is also compressed so that it is smaller. Problems arise when the sound is compressed so much that you start to lose quality and fidelity.
File Formats and Codecs (compressor/decompressor) are used to make the sounds smaller. Some of the most common are Windows Audio wav, mp3, mp4, m4a, Windows Media Audio (wma), Ogg Vorbis (ogg), Monkeys Audio (ma), flac, Apple's Advanced Audio Codec (aac) and many others.
Converting Audio
If you save out a WAV sound the file can be pretty large. I prefer to compress my audio with the Free Mp3 Wma Converter from koyotstar.free.fr/indexEn.html. Great software and very easy to use. Just drag the file into the "Files to convert" window where it will be listed, change the "Output configuration" settings, and Convert! Easy!
Almost all audio editors also have the ability to save or export audio in different formats and codecs.