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# Audio125 wk1-review-digital-audio-specs-and-acoustics

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### Audio125 wk1-review-digital-audio-specs-and-acoustics

1. 1. The Sound Wave Four Parts Compression – most pressure Rarefaction – least pressure Amplitude = volume/loudness Wavelength = pitch/frequency
2. 2. Pitch & Frequency Pitch = relative highness or lowness of sound Frequency = number of cycles per second One cycle = 1 compression + 1 rarefaction Measured in Hertz (Hz) and Kilohertz (kHz) 100 cycles per second = 100 Hz 1000 Hz = 1kHz
3. 3. The Audio Range Normal audio range utilized in professional music/audio applications? 20 Hz ~ 20 kHz Normal hearing range? 35 Hz ~ 16 kHz By age 50, most people only hear up to 10 kHz
4. 4. Musical Pitch Middle-C = 261.63 Hz A440 = 440 Hz A = only whole numbers on the piano Octave Identification Middle-C = C4 (traditionally) C3 in Pro Tools and Logic; C5 in FL Studio
5. 5. Wavelength Higher pitch = shorter wavelength Lower pitch = longer wavelength
6. 6. Octave Up an octave = frequency doubles Down an octave = frequency halves
7. 7. Frequency Spectrum 10 audible octaves in the audible frequency spectrum 1st octave = 20-40 Hz 2nd octave = 40-80 Hz 3rd octave = 80-160 Hz 10th octave = 10,240-20,480 Hz
8. 8. PhaseDigital audio waveforms can be in phase or outof phasePhase can be constructive or destructiveMeasured in degrees One cycle is equal to 360 degrees
9. 9. Phase (cont.) In phase waveforms = added amplitude, louder volume Out of phase (partially) = reduced amplitude Out of phase (completely) = no sound
10. 10. Timbre Timbre = characteristic quality of a sound Sine wave = pure tone with only 1 frequency Most sound contains multiple frequencies Sine wave does not exist from acoustical instruments
11. 11. Timbre (cont.) Fundamental = bottom “core” frequency of a sound Partials = frequencies that exist above the fundamental Harmonics vs. Overtones
12. 12. Sound Envelope Attack Decay Sustain Release
13. 13. Acoustics The science of a sound wave‟s behavior as it travels through an acoustic environment Generation Transmission Reception Effects
14. 14. Acoustical Sound Unrecorded acoustical sound is omni-directional Three dimensional – depth, width, height Stereo sound = Lateral Two dimensional = depth, width How do we create depth in a stereo recording?
15. 15. Direct vs. Indirect Sound Direct sound = reaches the listener first; comes directly from the sound source Indirect sound = reflects off of one or more surfaces before reaching the listener Early reflections Reverberation (Reverb)
16. 16. Studio Design Recording Stage/Booth Acoustic treatment must be appropriate to the music being performed Isolation Booth (Iso Booth) Little, or no, reverb Control Room Acoustic treatment must be appropriate for the mixing/mastering/monitoring experience
17. 17. Room Acoustics Reflect Absorb Reflect & Absorb Diffuse (Diffusion) Diffract (Diffraction)
18. 18. Reflection The angle of incidence is equal to the angle of reflectance Rooms with flat parallel walls are more prone to unwanted reflections Change the angle of one or more walls to compensate
19. 19. Absorption Sound is almost never completely absorbed; usually absorbed and reflected Types of Absorbers Porous/Foam absorbers Foam corner blocks (aka „bass traps‟) Diaphragmatic/Helmholtz absorber
20. 20. DiffractionSpreading of asound through anopening oraround an object
21. 21. Diffusion To scatter or distribute sound evenly Sound approaches a diffuser in one direction, but it scattered evenly throughout the room
22. 22. Types/Shapes of Diffusers
23. 23. Monitoring Symmetry & Tips Speakers should be equal distance from walls and corners at an equilateral triangle to the monitoring position Avoid putting monitor backs too close to walls (if your room is big enough) Back/side wall diffusers work well to scatter reflections If your room is too small, put diffusers behind the monitors Square room = bad = more resonances
24. 24. Monitor Vibrations AuralexMoPads Reduce vibrations from setting monitors directly on desks Angle monitors down if desk is too high
25. 25. Why all the fuss? Why all the fuss about proper acoustic treatment? What‟s wrong with my bedroom/apartment? All sounds are a product of their environment Every mix will sound different based upon the proper (or improper) acoustic treatment of a room Better acoustics = more accurate mix = better mix = less work for you
26. 26. Analog Recordings Signal is continuous Voltage running from a mic to the Mbox Mbox converts to a digital format Time & Level = Wavelength & Amplitude
27. 27. Digital Recordings Numerical representation of analog sound signal‟s actual frequencies and amplitude Sampling = number of discrete values taken per second Quantization = number of digital „levels‟ of information
28. 28. Sampling/Sample Rate Number of samples taken per second Some common sampling rates 32 kHz – broadcasting 44.1 kHz – Red Book CD format 48 kHz – digital video recorders / DVD-audio 96 kHz – DVD-audio The higher the sampling rate, the higher the frequency range
29. 29. Bit Depth (Resolution) Describes the number of bits of information recorded for each sample CD = 16-bit DVD = up to 24-bit The higher the bit depth, the higher the dynamic range More mix “head room” Does not affect frequency range
30. 30. Audio Quantization & Binary Code The bit depth determines the number of bits of information taken per sample 16-bit signal = 216 = 2x2x2x2x2x2…. (16 times) 216 = 65,536 possible combinations between 0000 0000 0000 0000 and 1111 1111 1111 1111
31. 31. AQ & BC (cont.) Bit depth determines the number of “Quantization Levels/Layers” Example of a Sine Wave at a 2-bit resolution
32. 32. AD & DA Conversion ADC = analog-to-digital converter DAC = digital-to-analog converter What converts a signal from analog to digital can be a number of devices: Digital mixer with mic/line inputs Audio interface = Mbox/002 Sound card in the computer CD/MP3 player
33. 33. Digital Audio Workstations Digital Audio Workstations (DAW) Record, edit, and playback Computer-based DAW (ex: Mac + Mbox + Protools) Processing, mixing, and manipulation handled by the computer Sound card or audio interface needed to input/output audio Integrated DAW (ex: BOSS BR-1600 CD) Software, console, and control surface are an all-in-one unit
34. 34. Audio Formats Uncompressed – WAV, AIFF, CAF, AU Lossless Compressed – FLAC Lossy Compressed – MP3, OGG, AAC, M4A, WMA
35. 35. Uncompressed Files in Practice WAV and AIFF (uncompressed) are the file types that are generally worked with They are “Flexible” file types that can handle any Sample Rate / Bit Depth combination Audio Recording software does NOT directly record to compressed formats
36. 36. DAWs& Audio Data Rate Audio Data Rate = defines the flow/size of data within an uncompressed format (WAV/AIFF) AKA „Bit Rate‟ Red Book CD = 16-bit x 44,100 Hz 705,600 bits of information per SECOND
37. 37. DAWs and Sample Rate Most DAWs can support files with multiple bit depths DAWs cannot run multiple files with different sample rates simultaneously The sample rate of the project must match the sample rate of the files in the project, if not, the files will not play at the correct playback speed
38. 38. Sample Rate &Nyquist As said before: The higher the sample rate, the higher the frequency range of an audio recording Nyquist Frequency Half of the sample rate Determines the highest frequency that can be accurately reproduced in an audio recording CD Sample Rate = 44,100 Hz Nyquist of 22,050 Hz