Not as loud as a normalized audio (-1/+1). Note that if the uncompressed audio stream is a stream of numbers between -0.5 and +0.5 (as reported by audacity), the MP3 should reflect this level and your smartphone will convert the stream back to -0.5 and +0.5. Since MP3 compression is lossy, don’t expect the same loudness exactly. Try to convert the MP3 file back to a WAV file (CD audio), and you should roughly get the same loudness. (A simple A4/440Hz will have a relatively high precision on the 440Hz, and less on neighbours frequency which should be masked by your ears). If you compress this stream in MP3 and decompress it (you can’t send an MP3 uncompressed directly to the sound card), you have still a stream of numbers between -1 and +1, but you can’t consider a bit depth, because the precision is degraded differently according to the frequencies. If you have a file with higher numbers (with floating point numbers typically), they can’t be played on the soundcard without clipping (a degradation of the sound). The sound card which uses a comparable coding scheme is not compatible too. The CD coding scheme is not compatible to higher set of numbers. On audacity, each number is matched with a number between -1 and +1 (it is a pure convention, the program could have printed -100%/+100%). It is a stream of 16 bits samples : in an other word, a stream of numbers between -32768 and +32767. What does it mean? Is there a way to increase that dynamic range? Side question: In audacity a file is created with +1.0 / -1.0 range. Where is it defined? How a player knows how loud to play, what level of output level to make? Therefore I do not see a base loudness level is defined in metadata. That would support metadata and obviate the need for tags. Tag formats for MP3 files, nor is there a standard container format Metadata such as the title, artist, album, track number or other
Non-PCM formats, such as lossy compression formats, do not haveĪ "tag" in an audio file is a section of the file that contains Butīit depth is only meaningful in reference to a PCM digital signal. On Digital audio wiki page again I did not find info about loudness, but guessed Audio bit depth might play a role. In MP3 wiki I did not find info about how loudness is defined. I've tried google search and results advice to use some gain apps, but I want to understand the theory first. Smartphone has amplification buttons, but at same level different files` sound is much different by loudness. Say there are mp3 files and a smartphone. Still trying to understand why loudness data is so difficult to find.
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