About Pitch Correction Plugins

Since the introduction of Antares Auto-Tune, in 1997 [1], pitch correction algorithms have considerably changed popular music and music production. This technology allows producers to change the intonation of a vocal performance to be perfectly in tune, based on a tuning reference (usually A-440 Hz). The wide dissemination of pitch correction plugins, from different vendors and at all price ranges, have made this technology easily available for professional and amateur producers.

In the present day, it is possible that the majority of popular music recordings use pitch correction algorithms, to some extent [2]. New products, like Melodyne, allow producers to go even further and manipulate not just pitch, but intensity, duration, breath sounds, etc. These new technologies have changed the paradigms of music production, and are subject to a lot of criticism, since it is possible to make an unskilled vocalists performance — even one with big intonation problems — perfectly in tune.

On the other hand, pitch correction can be really time saving, for example, when you have an awesome take with some minor intonation issues, and you don’t have time or budget to redo the recording. Tools like Melodyne also enable producers to create vocal harmonies from the original take, with no need to record any extra voice, which might reduce the production costs considerably. Even though the recording might loose some of it’s potential in terms of expressiveness, it can come in handy in certain situations where you don’t have a singer available to record an extra voice.

Another common use of pitch correction is for manipulating the voice sound itself, creating an effect that sounds a bit like a ´robotic voice´. This particular use of pitch correction was made famous by the 1998 hit Believe, from Cher (see below). Since then, many other artists have used it in a similar way, specially in electronic music genres.

In conclusion, the use of pitch correction algorithms such as Auto-Tune and Melodyne have become widely spread. It changed popular music in several different aspects, and it keeps changing as new technology becomes available. Even though there is lot of criticism around it, it can’t be denied that it is a useful technology, and that it’s use can’t neglected by music producers.

References

[1] http://www.antarestech.com/about/history.php

[2] https://worldpopmusics.wordpress.com/casestudies/pitch-correction/

Converting Audio Files Using Mac OS X Terminal

I just figured out Mac OS X has a nice command line utility to convert audio files called afconvert . This is a great way to do batch audio conversion with total control over what you’re converting. The basic syntax is:

afconvert -d DATAFORMAT -f FILEFORMAT INPUTFILE OUTPUTFILE

To list the data and file formats supported, simply type:

afconvert -hf

The following script lists all the AIFF file on a directory and converts them to WAV.

ls *.aiff | while read file
do
afconvert -d LEI16 -f 'WAVE' $file `echo $file | sed 's/.aiff/.wav/'`
done

Sound: Propagation, Amplitude, Frequency and Timbre

Propagation
Sound waves travel in air through the compression and rarefaction of air molecules. This compression and rarefaction happens in the same direction the sound travels. Therefore, sound propagates in air as a longitudinal wave.

However, sound propagates through solids in a different manner. In a string, for example, the vibration propagates as a transverse wave.

The speed of sound depends on the properties of the material through which the wave is traveling. Differences of temperature or air pressure can affect the speed of sound in air. In dry air at 20 °C the speed of sound is 343.2 m/s.

Amplitude
Amplitude represents the intensity of the sound wave and is related to the volume of the sound (though it is not exactly a direct relation). If the average square of the amplitude of a sound wave increases, the volume perception will also increase. In fact, the energy of a signal can be calculated using its’ amplitude.

Brief and drastic changes in amplitude might not cause a big change in volume perception, but they do cause an audible click. This sudden change in amplitude is known as pulse.

Frequency
The frequency of a sound wave traveling in air is the number of cycles of compression/rarefaction per second, and is measure in Hertz (Hz).

Although in real condition there are always multiple different frequencies traveling together in a sound wave, there is a fundamental frequency, which is usually the lower frequency of that sound wave, and it’s related to the perceived pitch. Basically, the higher the fundamental frequency is, the higher the perceived pitch.

Timbre
The perceived timbre of a sound wave depends on multiple factors, and probably the most important of them is the distribution of the harmonic partials of the wave. The harmonic partials are basically frequencies that are integer multiples of the fundamental frequency of the sound wave. The image bellow shows the harmonic partials of a vibration propagating in a string.

The timbre will be different according to the distribution of intensities between the harmonic partials of a sound wave. The image bellow shows the difference in the distribution of the harmonic partials for two different music instruments: a guitar and an alto saxophone.