When converting anything to MP3 such as audio cassettes or any digital audio files it is important to keep in mind that MP3 is a format primarily for access. It is not a format to use as the target format when digitizing your audio cassettes to preserve them long term. Why does this happen to be the case?
Well, MP3 is a format that uses compression. Compression means that audio information is irreversibly eliminated when the file is created in order to save storage space.
This is not ideal when you want to make a digital copy which will likely serve as the master recording in the future. You want to ensure that every detail that exists in the original analog audio cassette recording is faithfully captured or at least captured to the greatest extent possible. MP3 does not do that. The other problem with using a compressed file format such as MP3 is that future conversion into other types of files will not result in the best recording possible. Converting anything to MP3 and then to some other digital file in the future will result in a recording that can be quite different than the original analog audio recording that was digitized and may contained audible artifacts.
Ideally, when converting an analog audio cassette or analog audio reel recording to digital, it is recommended to use the WAV file format or the related BWAV (broadcast wav) format for long term preservation of the audio content. The WAV format does not use compression and so all the information captured from the original analog recording is maintained. The other advantage is that there is greater flexibility going forward and many other types of files can be made from the WAV file without much quality loss. Ideally, make a WAV file first and keep this as the master file and make MP3 files from the WAV files.
So, why is MP3 file format used and why do people pretty much convert anything to MP3 these days. The main reason is for access. MP3 files are smaller in terms of storage capacity than WAV files. Because of this smaller capacity many audio files can be stored on storage media or portable devices. With WAV, a substantially smaller amount of files can be stored and for many this is unacceptable for flexibility and access. Despite the small file size, MP3 still can provide very good audio quality in some cases. This is another reason why many are converting anything to MP3 – small file sizes and good quality or at least good enough for most listeners’ needs.
In terms of storage capacity, what is the difference between WAV files and MP3 files?
Typical digitization to a WAV file is performed at 44.1 kHz sample rate and 16-bit of bit depth. These are the digital settings for an audio CD. For preservation of oral recordings these can be acceptable but some prefer increasing the bit rate to 24-bit. For high quality music recordings, the settings used are generally 96 kHz sample rate and 24-bit for the bit rate. The storage capacity required for 1 hour of a stereo recording at these settings is:
Note that only the first option will allow one hour of digitized audio to be stored on a CD. The other options will require storage on other media that has more capacity such as DVD, Blu-ray, hard drive, or flash media.
Many different settings can be selected when digitizing anything to MP3. Examples of the capacity required to store one hour of audio at various settings are provided below:
As you can see, even at the highest MP3 bit rate, one hour of music in MP3 format requires much less storage space than one hour in a WAV format. As a final example, on a typical CD at the CD specifications for sampling and bit-rate (44.1 kHz and 1411.2 kbit/s) you can store about 19 songs of about 3 and half minutes each. For MP3, you can store the following amount of three and a half minute songs on a CD: