Ripping vs. Copying an audio file

Question

Lets say If an audio cd is not copy-protected. Since every drive has their own read offset and If use a CD Ripper then would I get the audio files with same checksum on different drive using a different computer? How is that different from copying it directly?

Answer 1

Copying would just copy the .cda files (Windows). Those are descriptor files containing the location of the tracks on the disc, just like a shortcut. They don't contain sound. Ripping involves actually copying the sound information, so you can play the music without the CD inserted.

Wikipedia on Windows .cda

Crash course on file formats: If you rip to a format such as MP3, WMA or AAC (MP4, M4A), the audio will be converted (lossily compressed), making the file smaller but losing some information. A format such as WAV usually would not compress, giving large files but a perfect copy of whatever is on the CD. Formats such as FLAC are losslessly compressed, giving a file size between the lossy and the uncompressed, but with the quality of the uncompressed.

• Note I'm using container formats and the contained data type (codec?) interchangeably to keep things relatively simple, see other sites such as Wikipedia here for more detail.

Answer 2

The audio on an audio CD is not contained in files, but in tracks. There is no real filesystem on a audio CD. When playing a CD, the CD is read sequentially and the bytes are immediately converted into audio.

When copying a file in the normal way, a part of the file is read and then that part is written to another file. When you would do that on a CD, the CD spins on while you are writing, so that you miss a part of the audio. With files, you can resume reading on the same position, but this is not possible with audio tracks. Ripping software overcomes this by reading a big chunk, writing it and then rewind the CD a bit to get the next chunk.

Answer 3

It seem the asker is concerned about drive read offset, which is nicely explained here. Therefore the other answers and comments (so far) are not directly addressing the asker's concerns. What the asker means is that if two CD drives with two different read offsets are used to rip the same audio CD into the same format (example MP3) at the same bit-rate and encoding settings (even on the same computer; it doesn't have to be different computer), will the ripped files produced be exactly the same? Or will they be different (giving different checksums) because of the difference in read offsets?

My educated guess to this is a NO, because the difference in offsets means the two drives will read of two different digital audio data for the same song, which when encoded to MP3 will produce two different MP3 files which sound the same to your ears but produce different checksums. MP3 encoding is simply a fixed computer algorithm and can produce the same file over and over again at same settings, but only with same input audio. In our case, the different read offsets means the input audio will be different for different drives (at least that's what I understand, but I'll need an expert to clarify).

Probably, the quickest way to objectively determine an answer to this is to actually use two different drives with two offsets and ensure you use a ripping software that doesn't apply offset correction (certain software applies an algorithm called AccurateRip, and there may be other algorithms).