How is the quality of audio file when PSNR is more than 48?

I decoded an mp3 file and save as wav file. Then I compared the two audio files (mp3 & wav) by using PSNR matlab (coding shown below). The results obtained are shown in the table.

Signal1 = audio.mp3;
Signal2= audio.wav;
[R C]=size(Signal1);
err = sum((Signal1 -Signal2).^2)/(R*C); 
MSE=sqrt(err);
MAXVAL=255;
PSNR = 20*log10(MAXVAL/MSE); 

How can I comment on the result?

According to the post here, it says ‘If the reconstructed audio signal is exactly same as original signal then MSE =0. And if Max pixel value is 255 (8-bit representation), then the value of PSNR = 20*log(255) = 48dB.’

Since the PSNR of the songs are more than 48, can I conclude that the decoded song (wav) has the same quality as the mp3 file?

Answer 1

[Raunak Gupta]

Hi,

In the code you have mentioned that

PSNR = 20*log10(MAXVAL/MSE);

This means

PSNR = 20*log10(MAXVAL)  - 20*log10(MSE);

Since for value of 1>MSE>0 the second term would become negative and hence add to the PSNR Value making it greater than 48dB. So, in conclusion the PSNR can go up to infinity for very low value of MSE. But for measurement of quality of decoding, higher the PSNR better it is.

For your case the PSNR values are on higher level so you may conclude the quality of decoding is good.