I'm not great at scratching, so please excuse the shoddy turntablist wannabe! The sample used is the over-used 'Aaahhhh' from the end of "Change the Beat" by Fab 5 Freddy (know your hip-hop history!). All scratching was done using my dusty old Vestax PMC 05Pro mixer (and not in-app cross-fader functionality) and recorded on a Korg M1 recorder in wav format...then crunched down to 320kbps mp3 for soundcloud. Each scratch snippet lasts about 30seconds, no beat just scratches of the same sample.
Here is the soundcloud pages with the scratches.
Vinyl - this was done as a control test and is the format I'm most used to, the turntable offers resistance against the fingers and so you should be able to get a decent flow going during a scratch session. I am using a Vestax PDX-2000 turntable.
CD - I figured that because we're comparing apps using mp3s it would only be fair to include a CD deck in here as well...using a cd containing the same mp3 as used in the apps. The CD deck spins round like the turntable but has a smaller surface however still very responsive and relatively easy to scratch with. I'm using a Denon DNS3500 CD deck (with latest firmware patch - it improves scratch responsiveness!). For those eagle eared (or maybe bat-eared) listeners, I know I've got some ground issues on the cd deck - identifiable by the faint hum in the background during cuts.
BabyScratch - OK, so this is the free app, however it claims to use the same sound processing as in the Flare and BabyDecks apps. These were the first apps to offer scratch capability and perhaps it does feel it now. The sound is quite distorted during slow movements, much more so than other apps tested. However, the main advantage for BabyScratch and Flare is that they are single deck, so on an iPad offer a larger surface area to scratch with. The deck responsiveness was pretty good, it seemed to hit a nice balance between not too slippery and not to slow. I'd recommend trying the free version first though!
BabyScratch is free!
DJay - the most expensive app offering scratch capabilities. The sound is much better than on BabyScratch, noticably so throughout even at slower speeds. The disadvantage here (when scratching) is that there is so much other functionality in the app, the space left for the decks is relatively small on an iPad. Also the deck seems to spin a little too far most times which leaves it feeling a little slippery and difficult to control during scratching. I found that using the side of the tip of my finger was probably best on this app to move the deck.
DJay is currently priced at $19.99 (full review here)
TapDJ - a recent app, like DJay offering 2 decks but a simplified interface - perhaps because other controls are off-page. The sound quality when scratching is (to my ears at least) equivalent or very close to that of DJay. The advantage over DJay for this app is that the space allocated for each deck is much larger, giving your fingers more room for movement. My initial impressions of this app were that it was pretty disposable and not a real tool for DJ use, however I am warming to it - but there are plenty of things that could do with changing (like offering a split cue option).
TapDJ is currently priced at $1.99