NED11: Module 10

Audio on the web
Background music can set an emotional tone, dialogue and narration can supplement written passages. Sound effects can also be used for interactive functions suck as button clicks.

Terminology of audio:

• AAD - Analog Record, Analog Produce and Digital Master
• ADD - Analog Record, Digital Produce and Digital Master
• DDD - Digital Record, Produce and Master (this format is the cleanest
• Bits are like digital information - zeros and ones. The more bits the more accurate the sound reproduction
• Sample Rate and Bit Depth - the higher the sample rate and bit depth recorded, the better the quality 8 bit sound uses 256 amplitude levels while 16 bit sound uses 32,768 amplitude levels
• Compression (ie MPEG) uses lossy compression that strips out sounds that are not discernible to the human ear to achieve very high compression ratios while maintaining near-original sound quality.

Audio Tips and Tricks:

• Keep everything DDD if you can
• Make sure you normalise your files. This trims off amplitudes above or below certain levels. and leaves you with a steady and stable signal
• Use a good pair of headphones or speakers while editing sounds
• Equalise your files, this ensures proper ratio of treble to bass. Be careful with bass - some smaller computer speakers can't handle it very well
• Test your audio on different systems
• Keep it simple, resist the temptation to get carried away with all the special effects
• Use the best equipment possible 

How to keep sound files small for quicker downloads:

• Keep the length of your audio clips short - the shorter, the better
• Limit the number of channels you use - mono is half the size of stereo
• Reduce your bit depth to only what you need
• Keep your sampling rate down - 22.05kHz is half the size of 44.1kHz
• Voice only files can be reduced down to 8kHz without any discernible loss in quality while music will sound acceptable at 22kHz

Googling 'sound effects' produces many websites where you can obtain sound effects, many are free. However if you decide to record sound effects yourself, some software suggestions are QuickTime, Bias Peak, Sonic Foundry Sound Forge and GoldWave Audio.

Using sound in your document:

• Let the user have the option of turning off or adjusting the sound volume
• Choose the right voice talent for any planned narration. The wrong voice. accent or inflections can seem inappropriate or even grating to the user
• Choose sound effects wisely, and only use those sounds that add meaning to your project

Online delivery strategies:

Non-streaming audio must be downloaded before playback and usually results in larger files. File formats include:

• WAV - originally developed as the standard audio format for Windows but is now supported on Macs. Most commonly used at 8kHz to 11.025kHz at 8 or 16 bit
• AIFF was developed as Mac standard but now supported on PC. Most commonly used at 8kHz to 11.127kHz at 8, 16 or 32 bit. Similar performance to WAV
• MPEG - maintains pristine sound quality at compression rates as high as 10.1. The higher the number, the more complex the coding and the more powerful a processor you will need to compress and decompress
• MIDI was originally developed as a standard way for electronic instruments to communication with each other. They are a mathematical command that describes a series of notes. MIDI files are incredibly compact and are capable of packing a minute of music into just 10K which is 1000 times smaller than one minute WAV file. Unfortunately MIDI's can only contain notes, not real sounds.

Non-streaming advantages are they don't require a special server and they are simple to create audio flew in standard formats. The disadvantages are file size which can result in unacceptably long wait times for files to download and start playing. Because the audio file is being downloaded to the user's computer - it is difficult for artists and publishers to limit distribution and protect copyright.

Streaming Audio begins playback almost immediately. There are 3 components to streaming audio - the Encoder (used to create the file format), the Player (used by the user to hear the audio) and the Server Software (used to provide optimum streaming). Other advantages are the sound quality doesn't need to be severely sacrificed and artists and publishers can control distribution and protect copyright because the file doesn't get copied to the user's computer. The disadvantages however are the high cost of server software and the sound quality and stream may be affected by low speed or inconsistent Internet connections.