Effects based on Delay that vary over Time

Lets start with the beginning of audio effects. The first effect we can find the first effect that developed was during the 20 century: on the radio. Otherwise, it wasn’t a professional effect; they were imitations by people who did the sound effects in front of the microphone. That was because they didn’t really need sounds, just when the dramatic pieces started to develop more importance, they realise about sound effects and started to create them.

During that time the sounds were classified by two categories:

  • The sound/resonances that move on or help to the movement in the sequence of events.
  • Fixed sounds, the ones that were produced by a combination of manual and registered sounds.

Next audio effect that is of importance is the delay, it means: multiplying and delaying the modulation of signal sound. When the signal is processed we’ll mix it with the original signal. The result is going to be the classic echo sound.

  • example of delay

The parameters of delay are:

-Delay: it is the time that is spent to be slow in producing an echo, it measures in milliseconds or it synchronizes with a tempo.

-Feedback: it’s the amount of times that the sound signal is repeating, could be any value between one and infinity.

-Mix: It’s the amount of delayed signals that mix it with the original.

Those are the basic parameters for any delay modulation, but not the only ones. There exist more advanced ones, which are more controllers like; frequencies down in the time, adjust different echoes, MIDI synchronisation and frequency filtering.

Different delay effects and modulations exist such as in digital and in analogic. The further focus of the report is on the following four delay effects: Flanger, Phaser, Wah-Wah, and Chorus

What is Modulation?

Modulation is the process where parameters of a sinusoidal signal (amplitude, frequency and phase) are modified or varied by an audio signal.

Amplitude Modulation — Wah-wah, Phaser

Phase Modulation — Vibrato, Chorus, Flanger

Wah-wah: A band pass filter with a time varying centre (resonant) frequency and a small bandwidth. Filtered signal is mixed with direct signal.

A phaser is implemented with a notch filter replacing the band pass filter. A variation is the M-fold wah-wah filter where M tap delay band pass filters spread over the entire spectrum and change their centre frequencies simultaneously. A bell effect can be achieved with around a hundred M tap delays and narrow bandwidth filters.

Flanger

We could understand flanger as a mix between chorus but with a shorter signal delay, rarely perceptible, and phaser but with a LFO low frequency oscillator who is going to send into the delay input.

It produces a change of faze, not in an exponential (like in a been when we delay the signal and threated with LFO, this change isn’t necessary for all the frequencies. The effect should apply in mid frequency and high frequency.

Depth: it’s the amplitude of the signal, which has been altered (not original) so that, the greater the amount of the parameter, the greater, the alterations signal undergoes phase and has a clearer sound effect.

Rate: is the frequency that the modulation occurs; the time that the waveform is shifted.

Delay: the amount of delay is applied to the signal delay in ms. For more than 15 ms delay it becomes almost flanger chorus. 

Flanging — continuously varying LFO of delay,

Chorus — multiple copies of sound delayed by small random delays

Chorus

In Chorus the key is the delay. The original sound is mixed with the signal that has got through an oscillator of low frequency (LFO), which causes an effect of tuning.

All the signals have a delay, expect the original, and generate then a continual signal with more power/which is more powerful. Furthermore, the alteration can be lower or higher, doing the sound looks like more untended and unreal.

When using the lower parameters of LFO, in the Chorus mode will just occurs a simple delay.

Chorus is imitating a natural way through the use of the amplifiers; which is one thing that suffers delay and eliminates the LFO chain, differentiate harmonic distortion (especially when using valve) and generates two different frequencies.

The delay makes our ear listen to a false second guitar, for that reason, chorus is one of the most common techniques of the professional guitarists.

The phaser

Especially popularized by the great guitarist Van Halen is an effect widely used, but its foundations are poorly understood. At the hearing, phaser looks like a sweep signal, sounded like the blade of a helicopter or a wind tunnel. Technically its principles are discussed throughout the manual and network, saying in some places that the effect is a “soft” flanger, and talking complete phase cancellation in other cases.

In the case of phase, the signal is altered by reversing the phase and is barely delayed, causing these cancellations signal, and the ear receiving the long awaited effect of “sweeping”. Cancellations signal are different, with an exponential basis in the case of the phaser.

The main values ​​that we find in this effect are:

Speed: is the same parameter than chorus and measures the rate of change in phase, making that sweeping sound that occurs more or less obvious to the ear.

Intensity: In this case if we find something that is confusing, because the modulation phase we don’t need necessarily be 180, one of the problems that in the literature are mixed either effect as if they were the same. Still, cancellations continue to be produced at an exponential level, so many frequencies would not be affected.

Prezi file:

http://prezi.com/wmbkxjafzghr/effects-based-on-delay/

Sources:

http://www.cs.cf.ac.uk/Dave/CM0268/PDF/10_CM0268_Audio_FX.pdf

http://www.thomann.de/es/onlineexpert_page_guia_online_para_pedales_de_efectos_de_delay_otros_efectos_basados_en_el_delay.html

http://es.wikipedia.org/wiki/Delay

http://www.guitarristas.info/tutoriales/efectos-repeticion-reverb-delay-eco-ii/3290

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