[Neblix]

Does it matter whether I use E minor or D minor in a song?

[DJ SymBiotiX]

the only thing that matters is if you use A minor in some sort of adult film. Don't do that.

[Moseph]

Originally Posted by Neblix

Does it matter whether I use E minor or D minor in a song?

Only if the instruments you're using sound better in one key's range as opposed to the other's or if real instruments are going to be playing the music and one of the keys works better for technical reasons (ease of fingering, etc.). Or if you're not using equal temperament (but you are using equal temperament, so this is more of an aside than a consideration).

[Rozovian]

As the song's key or as a chord in it?

For the former, see Moseph's reply.

For the latter, harmony works better if you support the melody with the rest of the writing, using chords that contain many of the notes used in the melody. Depending on the key and scale (or mode) of the song, a D minor can be a chord using a note outside of the scale, possibly leading to clashing. While changing scales mid-flight can be done, it takes a bit of planning (or trial and error) to make it smooth. You ought to know this stuff already, tho.

[Garpocalypse]

What's coming before it?

really however you work the modulations is how you work them.

Dmin traditionally has been used as a funeral key. If something deals with or is to be used for something related to death then Dmin is used. Which can make it a great key for metal.

F#min is the best minor key anyway! and now the fighting begins...

[Fishy]

It only matters to listeners with synaesthesia and perfect pitch.

Other then that the range of the instruments chosen might affect it. For example the big epic chord should be E on guitars, but they should be C on a cello.

[DjATIO]

I think if you have vox in the song, consider which key is best for the performer. Otherwise, most people will not notice. If there is guitar, e minor is easier in standard tuning, d min is good for drop D tuning. Otherwise, it doesnt matter.. Try modulating the key back and forth to find out which one you like more.

[PROTO·DOME]

As in key or chord?

If it's key you're on about then no, not unless you're playing live; different keys are difficult for different instruments.

I'm sure it won't even matter to someone with perfect pitch, really.

However if it's chords you're on about then yes, it matters a lot.

EDIT -

Bah, you all covered it anyway. Whatever. This can stand as a testament to me knowing what I'm on about.

[Neblix]

Yes, sorry, i meant keys. Thanks for the answer. I previously thought it did not matter and that one minor didn't invoke a different mood than another.

[Skyline Drop]

Bb flat minor; the saddest of all the keys...