What is Virtual Bass Enhancement?

Virtual Bass Enhancement is a technique that is based on the phenomenon of Missing Fundamental. It is used in portable devices, because it is characterized by low cost, possibility of being used in devices with limited dimensions and it provides maximum bass performance.

The Missing Fundamental effect occurs in psychoacoustics and depends on the distortion of the wave propagating in the ear. This is because the human ear is non-linear and can cause audible distortion. If the record consists of harmonic frequencies for example: f1 = 200 Hz, f2 = 300 Hz, and so on, the frequency f0 has 100 Hz and is the fundamental one. This signal is perceived as a low sound even if the fundamental frequency is filtered out. This effect is presented in the image and in the form of listening samples.
First recording consist of a following frequencies: 100Hz, 200Hz, 300Hz, 400Hz, 500Hz; the second one has a tones at 200Hz, 300Hz, 400Hz, 500Hz. Can you hear the similarity?

Recording 1
Recording 2

In VBE an input signal is converted by adding harmonics to achieve the illusion of low-frequency perceiving. In addition, there are other algorithms which may improve quality of records. For example, they allow adjusting the volume of the sound which is heard subconsciously, they may decrease distortion heard, etc.

The majority of operations are based on psychoacoustic properties. Algorithms allow increasing the low frequencies without a signal attenuation. Moreover, it does not require any additional supply or a large-sized loudspeaker. The input signal is processed according to the following graph.


Frequencies with the value less than specified in the low-pass filter generate their harmonics according to a predetermined algorithm, and then they are converted to the signal with the signal components at frequencies higher than the limit-pass filter. Thus, psychoacoustic information is based on the whole spectrum of the output signal.

In order to achieve a better quality of recording, the amplitude of the harmonics is calculated based on the special formulas and loudness principles. The dynamics of the resulting signal is adjusted according to the equal-loudness contour.

It is able to increase low frequencies up to one and a half octave. All the frequencies are higher than the limit of the filter and can be heard from the speakers. Therefore, this idea is considered to be very effective.