When you make an MP3, you specify the “kbps” (kilo-bits per second).
Example: 128 kbps = 16 kilobytes per second. So regardless of anything else, 1 minute of audio at 128 kbps will be 60 x 16 = 96 kilobytes. (actually a tiny bit more due to metadata and other bits, but the audio data will be 96 kB for 1 minute of audio).
This means that 48khz only results in a larger file size in WAVs (and probably some other file types, but not mp3s)?
What I am uploading is a podcast and I see a lot of discussion about 44.1khz vs 48khz regarding file size. Does this mean they are not talking about mp3s?
Are there any quality differences between 44.1 and 48khz in mp3s and if yes, how are they conveyed if the file size is the same? Somewhere this additional information has to be stored, right?
MP3s may be “Constant BIT Rate” (CBR) or “Variable Bit Rate” (VBR)*
In the case of CBR MP3, the size of the audio data is totally predictable: “kbps x duration in seconds = size of audio data”
In the case of VBR MP3, the size of the audio data is less predictable as the encoder aims for a specified quality rather than an exact bit rate. The “Standard quality” setting usually gives around 170 to 210 kbps, but more complex sounds will tend to be bigger than simple sounds. The MP3 encoder automatically adjusts the bit rate to achieve the desired quality.
* There’s also “Average Bit Rate” MP3s, but they are fairly rare these days
I’ve not seen the discussion, so I don’t know what they are referring to.
Podcasts generally use CBR MP3 because some MP3 players have buggy support for VBR, which is a shame because VBR is better. Podcasters will want maximum compatibility.
For medium bit-rate CBR MP3, (example, 128 kbps), audio that is 44.1 kHz may give slightly better sound quality than audio that is 48 kHz.
Standard quality VBR MP3 will often produce smaller files with 44.1 than 48 kHz.
Interesting, this is not very intuitive. But I think I noticed that when I compared the 44.1khz and 48khz mp3s. I was confused because 48khz actually seemed to sound worse, particularly the intro soundtrack. But the intro soundtrack source file itself also had 44.1khz, so it makes sense to keep it at 44.1khz.
Regarding CBR and VBR, I’ve also noticed this because VBR made scrubbing not work properly in online players and the total episode length was off. This is what led me down this rabbit hole
Thank you very much for the clarification, that was very helpful!