First, it is important to understand that making a music album is more than just making music. The modern 'album' is something very recent – it has only been around for 60 years.
In my view, every album (or every proper, album-type album) is also a concept album of sorts. It doesn't need to have a narrative structure or present a cosmology, or even have the same theme (although it helps).
The exposition you are about to read requires at least a certain familiarity with certain bands and albums – I tried to use examples from fairly well known bands and artists, instead of using more obscure ones.
So, to be a proper album, you need three things (I wrote down three because it sounds legit, not because I have actually counted; I'm just telling you this for the sake of honesty – but if marketing taught us anything is that you are probably waiting for this awful sentence to be over in order to read what the three things are, so here we go):
Some people underestimate the importance of the title. The title is the bass line. The title sets the tone. And it imparts a certain mood. Imagine 'Dark Side of the Moon' was actually called 'Nick Mason Really Only Knows One Beat and Two Breaks' or 'Forward Momentum', or even 'Pink Floyd'.
It just wouldn't be the same.
The exception to the rule is, obviously, 'Sgt. Peppers...' (what a dumb name). But on the other hand 'Magical Mystery Tour' is even better and got, comparatively, no love. Why? The title is just as bad. In this case, it might have been better to go with 'We Now Take Acid Regularly'. But another reason 'MMT' (which actually sounds like the name of a psychedelic drug) didn't get any love (aside from being released with less marketing – which in itself proves the point) is:
This one is just as obvious. One should not judge a book by its cover, but since the saying stops there I think we're safe in assuming a lot of people do judge – at least initially – an album by its cover. Either browsing on Bandcamp or strolling through a record store you know that the first two things you are going to notice are: the title and the cover. Depending on the cover, and if you know the artist or not, you will probably notice it before the title – so 'Covers' should actually be point 1. Well, too late.
Having a proper cover will situate your album in the cosmos of musical experience. If you see a cover with werewolves dressed as nuns raping churches and sawing off arms of children I think you would be safe in assuming it's some form of heavy metal – even if the band is called the The Pacifiers and the title is 'Baby doo be gah gah'. If on the other hand you have a really young, semi-naked girl on the cover, you will know it's a former Disney teenage idol's album.
The cover tells you in pictures what's inside – or it should. For a proper album to exist, the cover has to match the content. It has to suggest the same feeling as the title and also translate into image the sound of the album.
Take 'Dark Side of the Moon' again. Imagine the famous cover art. And now imagine one with Peter Steele's asshole in it (this is actually a cover of a Type O Negative album – there's a funny story behind it). In case you don't know who Peter Steele is and don't feel like doing a google search, he's a really tall, vampire-looking kind of guy. Now imagine his asshole. On the cover of 'Dark Side of the Moon'. It would not really fit with the content (both lyrical and musical) of the album. And I doubt Pink Floyd would want you to associate their iconic album with another asshole (Roger Waters' joke).
Now we're getting to the good part. For an album to be a proper album it needs a certain sound. The words 'feel' and 'vibe' can also be used, but as what truly sets the vibe or the feel is the actual sound, let's just call it 'The Sound'.
Even if the music in your album is entirely instrumental, or doesn't have a lyrical connection (which, incidentally, could be the title of a french movie about lesbian members of parliament who recite poetry to each other as they perform ritual castration of younger, virgin female politicians – like all french movies, really – but I digress).
The sound is what binds it all together and makes it more than just a collection of songs. Even if you had a proper title and a proper cover but then each song sounded like it had its own recording session, miles and years apart, and each time you would throw away all your equipment, knowledge of production and arrangement and lost all contact with the already tested professionals of the field, it would not be a proper album.
It's the difference between Filles de Kilimanjaro and Bitches Brew – even though Bitches Brew took a lot of copy/pasting or precisely because of it - I'm not sure at this point.
Going back to Pink Floyd, for those who aren't into Jazz, 'Meddle is a great album, but it sounds disjointed, almost thrown together with tape. Same with 'Atom Heart Mother' (another great). They don't have 'a sound'. They have 'sounds', which don't quite cut together nicely, and thus break the feeling that you are appreciating one single piece of art, and instead suggests that you are listening to a playlist in shuffle mode.
So how do you attain 'a sound'? While the composition can help set 'the sound', the real magic happens mostly on arrangments, production and mixing. It's akin to drawing in black and white and then adding color.
I'll tell you all about it another time.