2. Contents :
• Introduction
• Time Domain Operation
• Frequency Domain Operation
• Advantages & Disadvantages
• conclusion
3. Almost all musical programs are produced basically in two stages:
1. Sound from each individual instrument is recorded in an acoustically inert
studio
2. Signals from each track are manipulated by the sound engineer by adding
special audio effects and then combined in a mix-down system to generate
the final stereo recording.
4. • Sound recorded in an inert studio is different from that recorded
in a closed space.
• Digital Filtering can be employed to convert the sound recorded
in an inert studio into a natural-sounding one by artificially
creating the echoes and adding them to the original signal.
6. Single Echo Filter
• Echo are simply generated by delay units.
• The direct sound and a single echo appearing R sampling periods later can be
generated by the FIR filter shown.
7. The impulse response and the magnitude response of the single
echo filter for = 0.8 and R = 8 are shown below
8. Multiple Echo Filter :
The FIR filter below generates a fixed number of multiple echoes spaced R
sampling periods apart with exponentially delaying amplitudes.
9. The impulse response of a multiple echo filter with = 0.8, N
=6, R =4, is shown below :
10. An infinite number of echoes spaced sampling periods apart with
exponentially decaying amplitudes can be generated by the IIR filter
shown below.
11. The impulse and magnitude responses of the IIR multiple echo
filter for R =4 and = 0.8 are shown below :
12. Reverberation
The sound reaching a listener in a closed space, such as a concert hall,
consists of several components: direct sound, early reflections and
reverberation
13. Reverberation
The IIR multiple echo filter by itself does not provide natural
sounding reverberations for two reasons:
1. Its magnitude responses not constant at all frequencies
2. The o/p echo density given by the number of echoes per
second generated by an unit impulse input is much lower
than that observed in areal room .
14. • Reverberation : composed of densely packed delayed and
attenuated echoes.
• 1000 echoes / sec are necessary to create reverberation.
• This number of echoes is generated by reverberator.
Reverberation
15. Reverberation
• IIR multiple echo filter and the reverberator are basic units that are suitably
connected to develop natural sounding reverberation.
• By choosing different values for the delays in each section and multiplier
constants it is possible to arrive at a pleasant sounding reverberation.
16. Flanging
• Is an audio effect produced by mixing two identical signals
together, one signal delayed by a small and gradually
changing period, usually smaller than 20 milliseconds.
• The digital filter structure shown below can be used to
create the flanging effect.
17. Flanging
• The delay unit develops time-varying delay β(n)
• By periodically varying the delay bet. 0 and R with low
frequency 𝑤 𝑜 Such as
β(n) =
𝑹
𝟐
(1-cos(𝒘 𝒐 n))
18. Chorus Generator
• The chorus effect is achieved when several musicians are playing
the same musical piece at the same time but with small changes
in the amplitudes and small timing differences between their
sounds.
• Can be created by a chorus generator from the music of a single
musician.
19. Phasing effect generator
Is produced by processing the signal through a narrow band
notch filter with variable notch characteristics and adding a
portion of the notch filter output to the original signal as
indicated below:
20. Frequency-Domain Operations
• The frequency responses of individually recorded instruments
or musical sounds of performers are often modified by the
sound engineer.
• These effect is achieved by passing signals through an equalizer
• The equalizer is usually formed by cascading first-order and
second-order filters with adjustable frequency responses.
21. Advantages
• An information can be conveyed, displayed or manipulated
• Perfect reproducibility-identical performance from unit to
unit .
• Guaranteed accuracy-accuracy is only determined by the
number of bits used.
22. Disadvantages
• Speed and cost can be expensive when large bandwidth signals.
• DSP designs can be time consuming plus need the necessary
resources (software)
• If only a limited number of bits is used due to economic
consideration serious degradation in system performance may
result.
23. Conclusion
The audio effects are artificially generated using various signal
processing circuits and devices and they are increasingly being
performed using digital signal processing technique.
R: Delay parameter R denote the time sound waves takes to travel from the sound source to the listener after bouncing back from the reflecting walls.
The parameter alfa where alfa < 1,represents signal loss caused by propagation and reflection.
