Please read the title of this post very carefully, perhaps read it again before you continue to read, it may help you from hours of pointless discussions.
You may recall last week we ran a story kindly shared by producer Frank Fillipetti on discussions around digital audio, bouncing audio and the confusion (myths) surrounding this. He was both clear and (forgive the pun) frank in his assessment.
On my social media feed this morning was a discussion started by a friend, another long time engineer and producer, who had been told by a mastering engineer he could not submit his files zipped up, in other words using any kind of data compression. We don't know the reason for this request, although my friend said he alluded to it having something to do with changing the audio. Of course he may have religious reasons, or he may have a very odd computer that does not open Zip files, there are some out there, some of the early IBM magnetic tape machines in the fifties can't open Zip files. However my friend was asking his peers what we thought, was it anything to do with altering the audio?
A point made in defence of the policy was that some ZIP files can get corrupted, that's entirely true. The fact is any file can get corrupted and I would counter that a corrupted ZIP file is likely to have an original that it was created from, whereas (as I found out yesterday) if the original file is corrupted and does not want to open then you may well be screwed, especially if you don't have a back-up.
Of course it may be the fact that ZIP files are often the weapon of choice for those hiding malware and other nasty shit, so for those wanting to maintain fully working systems then they may not wish to accept Zip files. Although again, anyone with that level of concern should be investing in up to date system protection.
One thing I want to make entirely clear is that this is not about mastering engineers, some of the smartest people I know in the business are mastering engineers, I'd much rather trust my mixes to them than me trying to use the various tools to do it myself. So this discussion is not about mastering engineers.
But to the question - will compressing your data change (or ruin) the audio?
A Bit Of Self Doubt
In fact watching this conversation play out made me even doubt myself, so I decided to use good old science to double check my own opinion on the matter.
So I took a stereo audio mix file and placed it on the Pro Tools timeline. I then took the same source file and zipped it up, then I unzipped it up and placed that into the Pro Tools timeline. Then I inverted the polarity of one track so that it was out of phase with the other and silence, zero, nothing, nada, zip (two puns in one article). So science tells me that the audio is identical, not a single bit has changed.
I thought what have I got to lose, so I took the zip file, threw it into a new folder, zipped that up and tried the test again... you know the punchline.
If you perform that test and you have silence, (measurable silence) see image at the top of this article then you have your answer, the audio is exactly the same. If you think your ears tell you something else then get your ears checked.
Data Compression And Compressed Audio
The key misunderstanding here is there are two types of of compression being talked about, data compression and audio compression - entirely different things. There is data compression which helps to reduce file size when moving data around, it was far more necessary some years ago than it is today with high speed internet, but of course if you can improve speed and data usage by compressing data then it makes sense, especially if you have a capped data plan with your ISP. Pro Tools' cloud uses data compression when moving the data between projects, this is to improve speed of upload and download and reduce file sizes on the Avid servers.
Then there is compressed audio which is different to data compression. Data compression will make the data file size smaller using data compression technology, effectively removing redundant information, there's a good article here on how data compression like ZIP works.
Audio file formats that reduce the size using formats like MP3, AAC and FLAC are an entirely different kettle of fish, there are both lossy and lossless formats, compression methods differ but all of them will change the nature of audio to one degree or another. If you want to know a bit more about what MP3s do to the sound then check out Ian Shepherd's article on MP3.
Of course we haven't even mentioned that we use the term compression when using compressors and limiters, so no wonder it gets confusing having at least 3 interchangeable terms being used for very different things.
So compress your data using lossless compression technology like ZIP in the knowledge that it remains unaffected, if you have any doubt then run the test yourself.