Just got some new wheels which should have DT DB spokes. I assumed all DB spokes would have a external taper which could be felt when running a finger along the length of the spoke. My spokes are a constant diameter along the length. Could they still be butted?

No. Spokes aren’t hollow, so butted spokes always have an external taper, though different brands have more or less obvious tapers.

DT comp are 2.0mm/1.8mm.2.0mm so not massively thinner in the middle but still noticeable. If you’re comparing to another wheel it might haves spokes that are 2.0/1.6/2.0. But yes, if they’re butted they’ll be thinner in the middle.

Do both sides feel straight gauge?

They are supposed to be DT Comps. Will have another look in the morning.

Cheers

DT have a very gradual taper and can look plain gauge.

Rub around the nipples and see if the shaft size changes.

IME the butts on DTs are perfectly noticeable by eye and by feel, but if in doubt: Get an adjustable spanner and tighten it until it just touches the middle section. Move it towards the end. If you can make it to the end you’ve obviously got a plain gauge spoke.

Also, if you’re on the lookout for being swizzed (I was once, in exactly the same way) then check the spoke heads. DTs will have a “DT” logotype stamped in them.

You can see the butting. you can often see it in wheel pics on ebay!

Here’s a wheel I built the other day, you can see the butted spokes.

It’s not as clear as some pictures you see, but I wasn’t taking a pic of it, it just happened to be in the background. They are very obvious. The ones in the pic are DT comp

If you cant see and feel it then its not butted. Its very obvious. What wheels were they? Custom builds? Are they even DT spokes (Its got DT stamped on the heads if it is)?

Fwiw dt comp (db) and dt champion (plain gauge) both have dt stamped in the spoke head. Butting on comps is less obvious than on other db spokes (as above its only 0.2mm thinner in the middle) but it is definitely detectable by hand or tool if its not obvious by eye.