Thought I would post this because there are a couple of things that I learned from it. I wasnt familiar with how masking and the Fletcher-Munson curve works.
"Graham Stephens
, Broadcast Consultant- Retired (2018-present)
Answered March 14, 2020
Quality-wise there is no comparison. CD’s are digital storage devices that store analogue music signals sampled at 44.1 KHz and a word depth of 16 bits giving a raw sampling rate of just over 1.4 Mbps (stereo). Ignoring the practical difficulties of developing a perfect filter in real life this sampling rate will give a frequency response roughly equivalent to the limits of human hearing of 20KHz. (Nyquist theorem).
MP3 or any of the other streaming players sample audio at 128Kbps typically. This is a reduction in bit rate of around 11x compared to CD and so at the 44.1 KHz sample rate corresponds to just 1.5 bits per audio sample.
How is this huge reduction achieved? It relies primarily on a feature of the human auditory system called Masking. The human ear cannot hear multiple frequencies. It only hears the most dominant frequency at any instant and ignores everything else. So MP3 throws away the redundant low level frequencies and only codes the dominant one. The choice of “dominance” is not linear either. The frequency response of the ear varies according to a function called the Fletcher-Munson curve which describes the sensitivity of the ear at any given frequency. You can look this up on Google and discover that the ear is most sensitive at around 2KHz.
So all of this audio processing makes MP3 files very compact and for average listners on average audio playback equipment such as ear pods or PC speakers you will hear very little difference. However try playing the same music through your expensive Hi-Fi audio system and the difference is obvious. The sound is “thinner”, vocals can show sibilance (distortion of hard consonants) and other audio deficiencies. Some Internet Radio music stations which generally broadcast at 128Kbps can sound appalling on certain material.
Horses for courses."
"Graham Stephens
, Broadcast Consultant- Retired (2018-present)
Answered March 14, 2020
Quality-wise there is no comparison. CD’s are digital storage devices that store analogue music signals sampled at 44.1 KHz and a word depth of 16 bits giving a raw sampling rate of just over 1.4 Mbps (stereo). Ignoring the practical difficulties of developing a perfect filter in real life this sampling rate will give a frequency response roughly equivalent to the limits of human hearing of 20KHz. (Nyquist theorem).
MP3 or any of the other streaming players sample audio at 128Kbps typically. This is a reduction in bit rate of around 11x compared to CD and so at the 44.1 KHz sample rate corresponds to just 1.5 bits per audio sample.
How is this huge reduction achieved? It relies primarily on a feature of the human auditory system called Masking. The human ear cannot hear multiple frequencies. It only hears the most dominant frequency at any instant and ignores everything else. So MP3 throws away the redundant low level frequencies and only codes the dominant one. The choice of “dominance” is not linear either. The frequency response of the ear varies according to a function called the Fletcher-Munson curve which describes the sensitivity of the ear at any given frequency. You can look this up on Google and discover that the ear is most sensitive at around 2KHz.
So all of this audio processing makes MP3 files very compact and for average listners on average audio playback equipment such as ear pods or PC speakers you will hear very little difference. However try playing the same music through your expensive Hi-Fi audio system and the difference is obvious. The sound is “thinner”, vocals can show sibilance (distortion of hard consonants) and other audio deficiencies. Some Internet Radio music stations which generally broadcast at 128Kbps can sound appalling on certain material.
Horses for courses."
