Why Is My MP3 File So Large?

The MP3 format is famous for preserving good audio quality while significantly reducing the file size.  But occasionally, an MP3 file just doesn’t want to budge and takes up too much of our precious disk space, leaving you shouting at the screen, “Why is my MP3 so large?”  However, there are one or two things you can try to potentially make that pesky file smaller.

The most common cause for a large MP3 file is that it was encoded at a very high sample rate.  While higher bit rates improve the audio quality, they also preserve more audio data, resulting in a larger file.  To fix the issue, reconvert the MP3 to a slightly lower bit rate encoding.

Before you rush off and try and reduce the sample rate to the bare-bones minimum, just know that you probably will hate the result.  That’s because the file size and audio quality are directly related.  You need to know at least a little bit more about how the MP3 format works if you want to successfully reduce the size.

Understand Audio Files And Bitrate

The first concept you need to wrap your head around is sample rate and bitrate because this bitrate is the most likely culprit behind your large MP3 file.

Sample Rate Explained

When a song is recorded from instruments, the computer takes an analog signal and converts it into a digital file.  It does this by taking several “snapshots” or samples of the analog audio. 

This is known as the sample rate.  The typical sample rate is 44.1 kHz, meaning that 44 100 samples are taken every second of recording.  The reason for this particular sample rate is a little complex, but in short, sample rates need to be twice as fast as the frequency range you are trying to capture. 

44.1 kHz is twice the frequency range that the human ear can hear, so you ensure high quality by sampling at that rate.  On the other hand, sampling at a lower rate can result in weird audio distortions. 

Bitrate Explained

When a digital audio file is compressed and converted into a format like MP3 or AAC, the file is basically broken up and put into little boxes of data called bits.  Bitrate refers to how many boxes are stored in that audio file. 

So, in other words, if an MP3 has a bitrate of 192 Kbps, it means that every second of that file contains 192 000 bits of data.   

The highest typical bitrate used by MP3 and other compressed, lossy formats is around 320 Kbps.  This is considerably lower than the bitrate of a CD-quality song, which is 1 411 kbps, which is why CD quality is better than compressed audio format quality.

The higher bitrate of the CD means that each second of audio contains considerably more bits of data, thereby improving the audio quality.

MP3 Conversions Loose Audio Data

Even though MP3s have much lower bitrates than CDs, the average listener cannot tell the difference between a high-bitrate MP3 and a CD, especially if the songs are being played through typical headphones or speakers. 

This is because the way that MP3s compress the audio data is exceptionally clever.   During the conversion process, the algorithm analyzes the whole song.  It identifies points of extreme frequency or over-duplication of data.  And then, this data is discarded. 

What makes this work so well is that the data discarded is usually frequencies that we can’t actually hear or that our speakers can’t play back.  Somewhat surprising is that you can discard quite a bit of data before the loss starts reducing audible quality. 

That being said, as you continue to reduce the bitrate, the MP3 algorithm will be forced to discard the audio data you can hear.  And as soon as this happens, you will start to notice an irritating reduction in quality.

How Bitrate Can Make Your MP3s Too Big

So at this point, you probably have at least a working grasp of the concept of bitrate and how it affects file size.  In short, higher bitrates mean a larger file size.  This means that the first step you should take in reducing your MP3s file size is to check what bitrate you used to convert it. 

Recent years have seen various streaming services compete to deliver the highest audio quality.  It seems that 320 Kbps has become the market standard for “high-quality” streaming audio. 

However, much of the noise around these higher bitrates is just that: noise.  Or rather clever marketing ploys.  Sure, 320 Kpbs is objectively higher quality than 224 Kbps simply because it contains more audio data. 

However, whether that higher quality translates to a better listening experience depends on several factors, like the speakers or headphones you use. 

The point is that you may not need to encode your MP3 at 320 Kbps, and by lowering the bitrate, you can save a lot of disk space.  

For example, the typical 320 Kbps file contains 40 KB of data for every second, or 2.4 MB for every minute of audio.  So, a four-minute song will take up around 9.6 MB of disk space.  If you drop the bitrate down to 224 Kbps, the file size suddenly drops to around 6.7 MB. 

Reduce The Bitrate To Reduce The MP3 File Size

This means that the solution to reducing your file size is relatively simple.  First, check what export setting you are using that reduces the bitrate.  However, remember that every digit you reduce the bitrate by means more data is discarded, and this will become noticeable as you drop below 192 Kbps. 

But, in some instances, you can go as low as 128 Kbps and still be OK.  Obviously, this will also depend on the type of audio file you are converting, along with your listening preferences. 

So, the key is to reduce the bitrate by as little as possible to maintain higher audio quality.  As for the sample rate, reducing it will run the risk of creating aliasing effects on the song, in which case it won’t matter how high you bump the rate.  All it will achieve is hearing the distortions more clearly.

Another question you need to ask yourself is why do want to reduce the file size in the first place.  If it is to save a few MBs of storage, then you probably have a bit of a storage crisis, which you aren’t going to resolve by dropping a few bits of data. 

Understandably, storage becomes a problem if it’s not just one problematic MP3 file but a whole library of music.  But in this case, slightly reducing the bitrates will also accumulate to save you a lot of space. 

However, if it is to send your song in for auditions, for example, then perhaps you should use a file-sharing platform like Google Drive or Dropbox instead of trying to email it.  This way, you can send in the highest-quality version of your song. 

Disks and floppy disks

Conclusion

The most common cause of large MP3 files is that the file was converted using a high bitrate.  Higher bitrates mean that more of the audio data is preserved, which increases both the quality and the size of the file.  So, to reduce your MP3 file size, you can reduce the bitrate.  Just be careful not to reduce it so much that you end up reducing the quality of the song. 

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