Reflection of Sound Waves

1. Reflection of Sound Waves • Sound waves reflect off of surfaces and return in a direction based on the angle of incidence

2. Reflection of Sound Waves • Sound wave intensity (level) is reduced with distance and each reflection off of a surface • More high frequencies are lost with each reflection • Amount of sound level and high frequency loss depends on the surface • Softer surfaces tend to absorb more high frequencies and sound level than hard surfaces • The longer it takes for sound waves to travel to surfaces, reflect then come back, the bigger or larger the room will sound

3. Reverb • The original sound as it reflects off of surfaces and decays is reverb • Any sound in a space or environment will have some reverb characteristics • Reverb provides a sense of room shape, size and material, and listening position in a room • Artificial reverb alters the room and sound reverb characteristics (adds reverb or changes reverb characteristics)

4. Reverb Characteristics Level First reflection Many thousands of reflections overlapping and blending (“reverb tail”) Time Early reflections Decay time Pre-delay

5. Reverb - Terms • Type– type of reverb or room (small room, hall, brick room, plate reverb, etc.) • Predelay – amount of time before the first reflection occurs • Decay time – time it takes for the reverb tail to fade to zero (T60 = time for sound to decrease by 60 dB) • Diffusion– time between reflections • Density– time between the initial reflections • Mix– blend or mix of wet (processed) and dry (original) signal • Frequency based settings – amount of high frequency loss, decay times based on frequency, etc.

6. Reverb Characteristics Level First reflection Many thousands of reflections overlapping and blending (“reverb tail”) Time Early reflections Decay time Pre-delay

7. Low Diffusion The reflections are far apart Can sound “grainy” Often works best with up-tempo or dense mixes Level Time

8. High Diffusion The reflections are close together Smooth sounding – a “wash” of reverb Often works best with ballads and open arrangements Level Time

9. High Density Close spacing of initial reflections A smoother sounding reverb for sounds with fast transient attacks Level Time

10. Low Density Far spacing of initial reflections Good for smooth sounds such as strings and sustained pads Level Time

11. Reverb Characteristics • Room size is controlled by the time of the pre-delay and reverb decay • Long pre-delay and decay times = Larger space • Short pre-delay and decay times = Smaller space • High frequency content indicates “hardness” of the room surface • Brighter (more high frequencies) = Harder surface (e.g., wood, stone, glass) • Darker (less high frequencies) = Softer surface (e.g., carpet, foam, fabric)

12. Delay Processors • A delay processor makes a copy of the original sound and plays it back • Control the time of the delay and number of times the copy is played • Used to create echoes or artificial stereo, or thicken sounds

13. Delay Characteristics First reflection Level Second reflection The distance between the reflections determines whether echoes or a thickening effect is heard Time Delay time

14. Delay Processor Terms • Delay time – amount of time between each echo or repeat • Feedback or regeneration – number of repeats or echoes • Mix– blend or mix of wet (processed) and dry (original) signal • Frequency based settings – amount of high frequency loss with each reflection, etc.

15. Delay Times • Distinct sounds – >25-35 msec delay time(can hear individual echoes or repeats) • Doubling or thickening – 15-35 msec delay time • Delay times in time with quarter, eight and sixteenth notes are usually the most musically pleasing and adds a more rhythmic feel • Knowing the beats per minute (bpm) is helpful • Can also use the tap tempo input on the delay processor

16. Delay Time Calculations in msec

17. Uses of Delay Processing • Used to thicken or double a sound (~15-35 msec delay times) • Thickening can be used to hide or mask slight pitch or timing problems • Used to add echoes or repeats of the original sound (>25-35 msec) • Used to create artificial stereo or panning • Add delay to a mono signal • Pan dry signal to one side and wet signal to the opposite side • Longer delay times = More stereo spread

18. Chorus, Flanging and Phase Shifting • Specialized versions of delay • Modulation continuously varies or sweeps the delay time • This speeds up or slows down the playback of the delayed sound • Results in slight changes in pitch and/or phase • Modulated signal (“wet”) is mixed with dry signal in various amounts

19. Chorus, Flanging and Phase Shifting - Terms • Delay time – time the signal is delayed • Depth, rate or modulation – adjusts the range or amount of delay time (pitch/phase) variation • Rate or speed – adjusts how fast the delay time (pitch/phase) changes (frequency)

20. Chorus, Flanging and Phase Shifting • Phase Shifting – medium rate times; 1-15 msec delay time • Flanging – higher rate times; 1-15 msec delay time • Chorus – slower rate times; 15-35 msec delay time • Stereo chorus – one channel is wet and dry mix; other channel is wet with inverted polarity and dry mix

21. Chorus, Flanging and Phase Shifting • Chorus – wavy, shimmering, moving sound; thickens • Phase Shifting and Flanging – hollow, swishing sound • Phase shifting tends to be more subtle than flanging