homogenous frame of mp3 audio file

i had done steganography process using mp3 file. i just using homogenous frame of mp3 file to hide secret message. so i change the bytes of homogenous frame with the bytes of secret message. then i compare the amplitude of both files using audioread function in matlab. but there is nothing difference amplitude value between both mp3 files (before and after steganography). is there anyone knows why homogenous frame of mp3 become special structure?i mean why the amplitude doesn't change even i change the bytes? i need a help. thanks

Answer 1

[Walter Roberson]

https://en.wikipedia.org/wiki/MP3

"MPEG-1 or MPEG-2 Audio Layer III,[4] more commonly referred to as MP3 (or mp3), is an audio coding format for digital audio. It uses a form of lossy data compression to encode data using inexact approximations and partial data discarding to reduce file sizes, typically by a factor of 10, in comparison with a CD while retaining a sound quality comparable to uncompressed audio. [...]

The MP3 lossy compression works by reducing (or approximating) the accuracy of certain parts of a continuous sound that are considered to be &beyond the auditory resolution ability of most people*. This method is commonly referred to as perceptual coding or "psychoacoustics".[9] It uses psychoacoustic models to discard or reduce the precision of components less audible to human hearing, and then records the remaining information in an efficient manner."

Basically, when the changes you make to the data are small, then mp3 might decide that they would not be noticed by most people, and so might discard them.

[Rini Indrayani]

Buti used fft to analyze the different. It's really had nothing change with the original mp3 before secret message embedding process. Then i tried to use heterogenous frame which the bytes in that frame has heterogenous bytes. So i change the bytes of heterogenous bytes with the bytes of secret message, then i do command "audioread" to get amplitude as i do when i used homogenous frame. The result shows that the amplitude changes. It's different with using homogenous frame that show no amplitude difference. That's why i asked if anyone know about the speciality of homogenous frame of mp3.