Kbps/file size relation to audio quality (.m4a)

palmsquare

Member
Sep 12, 2021
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Hi Im currently trying to wrap my head around audio quality. Here I have 3 different files of the same exact song in .m4a format. My understanding is that kbps will generally determine the quality. So how am I to understand the differences in actual file size? How can the lower file size seem to have higher audio quality even though it is the same file type?

Thanks for any help
 

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Welcome to the forum.
It's not my area of expertise but to my knowledge Kbps has nothing to do with quality it is a data transfer speed (kilobits per second)
Talking about .m4a files, they are smaller in size and have better sound quality over a wide range than any mp3 file. The .m4a is encoded with lossy Advanced Audio Coding (AAC), which enables it to provide the same bitrates as the MP3 yet having tighter compression. The compression aids the file to have smaller file size and helps deliver higher audio quality, or so I am led to believe so sound quality will be worse than a lossless file which will of course take up more space.
 
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Vincent Kars

Well-known member
Mar 6, 2021
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song in .m4a format.
No, m4a is not a format, it is a container.
You can put "anything" in it e.g. audio, video.

to my knowledge Kbps has nothing to do with quality
Depends.
If it is lossless compression, there is no relation with sound quality as nothing is thrown away.
If it is lossy compression, there is as the lower the bit rate, the lesser the audio quality will become as more and more information is thrown out.
ABX a 320 kbs MP3 with the original CD is hard, very hard. ABX a 64 kbs MP3 isn't
 
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palmsquare

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Sep 12, 2021
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Interesting thanks! So which file would likely have the higher quality? The one with the higher bitrate or the one with the larger file size?

Greetings
 

Vincent Kars

Well-known member
Mar 6, 2021
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Normally a higher bit rate is equivalent to a bigger file size.
Your screenshot is a bit puzzling as a 128 kbs should be more or less the half in size of a 256
In your case it is the reverse!

Without knowing how these files has been made, it is impossible to answer what is going on (unless there is a pile of art work in some and not in the others).
 
I thought mp4a
No, m4a is not a format, it is a container.
You can put "anything" in it e.g. audio, video.


Depends.
If it is lossless compression, there is no relation with sound quality as nothing is thrown away.
If it is lossy compression, there is as the lower the bit rate, the lesser the audio quality will become as more and more information is thrown out.
ABX a 320 kbs MP3 with the original CD is hard, very hard. ABX a 64 kbs MP3 isn't
I thought m4a was an audio only container, hence the a on the end
 
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Vincent Kars

Well-known member
Mar 6, 2021
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Correct, missed the "a" but even an "a' seems to be allowed to contain video as it is the same MPEG-4 fromat.
 
Correct, missed the "a" but even an "a' seems to be allowed to contain video as it is the same MPEG-4 fromat.
we aren't talking the same container it would appear and it hasn't really helpful in answering the OPs question.....
 

Jobb

Well-known member
Apr 29, 2009
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I think the 129 and 257 kbps files have a variable bitrate, whereby the 129 and 257 values are not maintained throughout, but only at the start of the file. They may be higher (or lower) later on.
Maybe you have an audioplayer that displays the current bitrate 'live', just to check this?
 

Vincent Kars

Well-known member
Mar 6, 2021
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270
Doing some calculations:
seconds * kbs /8 is the size in bytes
Compare this with the reported size


Secondskbsbits byteReported
168​
129​
21672​
2709​
12733​
168​
128​
21504​
2688​
2748​
180​
257​
46260​
5782,5​
6066​

The first is a weird one, reported size is way to big.
The other 2 looks fine assuming the kbs is a average rate (VBR).
I would keep the 257 kbs.
 

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