1. 1 Week 10: Audio Recording

2. 2 Overview  What is sound?  What does analogue mean?  Analogue-to-Digital conversion  Key terms in digital audio  Compression  Formats  Audacity demo  Practical work

3. 3 What is sound?  Sound is created when an object vibrates (moves back and forth), pushing the air around it  sound is a variation in pressure  pressure variations travel through air as waves (hence the term sound waves)  sound travels about 1000 feet/second

4. 4 What does analogue mean?  Analogue audio signal follows the same pattern as the vibration in air pressure caused by the original sound  Microphones turn audible sounds into electronic copies of those sounds  Pressure variations (sound) can be stored through:  Mechanical displacement (microphone, speaker)  Voltage variations  Wiggles in vinyl record grooves  Degree of magnetisation on tape  Optical density in film

5. 5  Have three attributes:  Wavelength  distance between any point on a wave and the equivalent point on the next phase (i.e. the length of the wave)  Amplitude  the height of each peak in the sound wave  higher amplitudes are interpreted as a higher volume  Frequency (pitch)  number of times a wavelength occurs in one second  measured in kilohertz (Khz), or cycles per second  higher frequencies are interpreted as a higher pitch Analogue wave patterns

6. 6  Audio systems are based around one simple concept:  take sound waves, convert them into an electric current and manipulate them as desired, then convert them back into sound waves  Transducer  converts energy from one form into another  microphones : convert acoustical energy into electrical energy  speakers: convert electrical energy into acoustical energy  Amplifier  a device which takes a signal and increases it's power (i.e. amplitude) Working with audio

7. 7  Process  sound source creates waves of sound (acoustical energy)  waves are detected by a transducer (microphone) which converts them to electrical energy  electrical signal from the microphone is very weak, and must be fed to an amplifier before anything serious can be done with it  loudspeaker converts the electrical signal back into sound waves, which are heard by human ears

8. 8 Digital to Audio Conversion  Measure an analogue signal periodically:  Store the measurements as a sequence of numbers

9. 9 Key terms  Sampling Rate  how often analog signal is measured  samples per second, Hertz (Hz) or kilo Hertz (kHz)  e.g. 44,100 or 44.1 kHz  Sampling Resolution  precision of numbers used for measurement: the more bits, the higher the resolution  bit depth  e.g. 8 bit (1 byte), 16 bit (2 bytes) etc

10. 10 Digital to Audio Conversion  The conversion process is not entirely perfect  Higher sampling rates produces closer fit (i.e. higher quality) at the expense of file size

11. 11  Humans hear variations from about 20Hz to 20000Hz Old samplers22.05 kHz (22050) DVD-Audio96 kHz (96000) DAT, DV, DVD-Video48 kHz (48000) UsesSampling Rate CD, DAT44.1 kHz (44100) Common Sampling Rates

12. 12  Bit depth Software (usually only for internal representation) 32-bit floating point DVD-Video, DVD-Audio24-bit integer CD, DAT, DV, sound files16-bit integer UsesWord length Low-res web audio8-bit integer Common Sampling Resolutions

13. 13 File Size  1 minute of CD quality audio  Sampling rate:44,100 samples per second (44.1 kHz)  Sample resolution: 16 bits (i.e., 2 bytes) per sample  Number of channels: 2 (stereo)  Gives  44,100 samples * 2 bytes per sample * 2 channels = 176,400 bytes per second  60 seconds per minute  60 * 176,400 bytes per second = 10584000 bytes ~ 10Mb per minute

14. 14 Compression  Audio compression consists of two parts:  Encoding  transforms the digital audio data in a WAVE file, into a highly compressed form called a bitstream  throws away data not required to reduce the file size  important to realise that the resulting compressed file is not the same as the original digital version - a close copy  Decoding  takes the bitstream and re-expands it to a WAVE file  Many different CODECS are available  MP3 is a common standard (!)  CODEC must exist on playback PC for decoding to work

15. 15 Common File Formats  WAV  AU  MP3  WMA  ASF  RA  AIFF Windows native file format Sun audio file (Unix) MPEG layer III compressed audio Windows media audio Microsoft advanced streaming format Real Audio compressed streaming data Audio Interchange Format File (Mac)

16. 16 Channels of sound  Mono  Stereo  Dolby Pro Logic  Dolby Digital 5.1 & 6.1 (Ex)  DTS 5.1& 6.1 (Es)  More information (data) requires larger file sizes  Specialist software to edit

17. 17 Where to get audio from  Copyright free audio  downloads available from module web site  magazine cover disks (credit source)  Internet (credit source)  Royalty free audio (purchase)  Media Tracks (www.media-tracks.com) $13 per clip  AKM Music (www.akmmusic.co.uk) £35 per CD  Partners in Rhyme (www.partnersinrhyme.com) free - $70 per collection  Create your own effects with Audacity  Premiere uses Smartsound to create seamless loops

18. 18 Hardware required to capture audio  Sound Card  Microphone  External devices  Mini disc  MP3 players  Keyboard  Speakers  headphones also useful

19. 19 Recording issues  Avoid background noise  Use a headset with an attached microphone for voice recording  leaves your hands free and keeps the microphone at a fixed distance from the mouth  Position the microphone to the side of the mouth, not in front  Check the sound levels

20. 20 Audacity  Free open source software  Easy to use  Multi-track editing  Effects  Convert between different audio formats  Supports industry standard VST plug-ins  (Virtual Studio Technology)  File type of.aup is the project file  contains all the edit instructions  need to export to create the audio file for playback  http://audacity.sourceforge.net http://audacity.sourceforge.net

21. 21 Audacity Interface  Video demo Video demo

22. 22 Tutorial  Devise the 250 word narrative/story for “Every house has its secret”  Record the story using Audacity  Edit into several audio clips for use in Flash  Use Audacity’s effects and mixing facilities + spot effects from…  http://mmedia.glos.ac.uk/mu110/audio.htm http://mmedia.glos.ac.uk/mu110/audio.htm  Develop the storyboard  Scenes  Sequencing within each scene  Swap with a partner  Review the storyboard and identify any unclear elements  Tutors will identify plenary items  Self Study  Review the storyboard and finalise with annotations  Review the Assignment Brief  Must include: 1 or more graphic characters, animation, audio to illustrate mood and change of pace  Begin building the scenes in Illustrator/Flash

23. 23 Any questions?