At the beginning of 2002 other compressed audio formats such as Windows Media Audio and Ogg Vorbis began to be massively included in programs, operating systems and autonomous players, which made it anticipate that the MP3 was gradually falling into disuse, in favor of other formats, such as those mentioned, of much better quality.
One of the factors that influences the decline of MP3 is that it has a patent. Technically it does not mean that its quality is inferior or superior, but it prevents the community from continuing to improve it and may force you to pay for the use of some codec, this is what happens with MP3 players.
New formats, such as OGG Vorbis, are not licensed, but are free SOFTWARE. That is why they can be used and improved without conditions. Even so, at the beginning of 2008, the mp3 format continues to be the most used and the one that enjoys the most success.
Mp3 – The psychoactive model and masking threshold
The psychoacoustic model and masking threshold
Compression is based on the reduction of irrelevant dynamic range, that is, on the inability of the auditory system to detect quantification errors under masking conditions.
The human ear has a perceptual masking threshold for its characteristics. If an airplane passes by us while we speak, the sound it produces is able to “cover” our voice. The same happens if a very strong DO note, on a trumpet, sounds at the same time as a pianisimo DO note on a violin: the DO of the trumpet, masks the DO of the violin, which is not heard.
This is due to the anatomy of the human auditory system: if two sounds of equal frequency are emitted, one with greater amplitude (volume) than the other, the sound of greater amplitude will mask that of amplitude (volume) than the other.
The psychoacoustic model is an average standard that divides the signal into approaching frequency bands, and then quantifies each subband based on the threshold of noise detection within that band. This model analyzes the audio signal and calculates the amount of noise that can be introduced based on the frequency, that is, calculates the “amount of masking” or
masking threshold as a function of frequency. Then, the encoder uses this information to decide the best way to spend the available bits.
Studies show that the distortion generated is imperceptible to the ear experienced in an optimal environment from 256 kbps and under normal conditions. For the non-experienced ear, or common, with 128 kbps or up to 96 kbps it is enough for it to be heard “well” (unless you have a high-quality audio equipment where the lack of bass is noticeably noticed and the sound is highlighted of “frying” in the treble).
In people who listen to a lot of music or who have experience in the auditory part, from 192 or 256 kbps it is enough to hear well. The music that circulates on the Internet is mostly encoded between 128 and 192 kbps.
MP3 – BItrate, CBR and VBR
CONSTANT AND VARIABLE BITRATE
CBR (constant bit rate)
It encodes the entire entire file with a single bit rate.
This method is the most common, and it becomes more predictable, always according to a file size and bandwidth. The file will be compressed to weigh a number of bits per second.
The bitrate is then measured in kbps (kilobites per second), the quality being better as much more bits per second weigh the file. In general, the most basic quality is
Around 128kbps, and the highest (for more educated ears) around 320kbps.
VBR (variable bit rate)
It encodes with a higher bit rate when the material is more complex, and a smaller amount of bits for simpler materials. By relying not only on the statistical references of the threshold of
average masking, but also of the source material, the .mp3 files compressed with VBR tend to be smaller than those compressed with the CBR method (they are the same quality) to have a more variable weight,
The quality is therefore no longer measured in kbps, but in levels (100 for the best quality – highest quality – and decreasing in the number for lower quality 10- lowest quality,)
