DanceMasters

Secret ripples are obtained by accessing the Parallel Universe in any given song (Standard or higher) and hitting ripples that are not visible. However, these ripples are indicated by a chime that sounds when a secret ripple is about to come. (There is no chime when playing on Stealth difficulty).

Originally, in order to get 450 secret ripples, you would have to unlock every single secret ripple in the game. However, when a free DLC pack containing Master difficulty was released, 150 new secret ripples became available.

The best strategy to unlock secret ripples is to play each song enough times to have a fairly good memory of the routine. Then start with Standard and work your way up.

Once a secret ripple is unlocked, a star will appear at the top of the screen. There are 5 secret ripples hidden in each song difficulty. The star that appears will indicate how far into the song it was located. For instance, if you see "--***", you know that the two missing secret ripples in the song are near the beginning.

The achievement basically requires you to gather 450 ripples across all songs in all difficulties, which means all the ripples if you don't have the Master difficulty DLC. So I'll be providing few important tips that will save you effort and time.

1) You should download the FREE Master difficulty DLC from the marketplace as Johnny mentioned.

2) If you fail a song after unlocking certain ripples, they will carry over and you won't have to get them again for them to count. However, if you pause the game and restart the song they will not carry over and you'll have to get them again. So, you might wanna save yourself the hassle of playing the whole song after unlocking a single ripple and just fail and start over, it will also help you memorizing the song.

3) I would recommend you to go for the ripples after you unlock all the difficulties, cause you'll want to work on them song by song, since they're the same moves but with different notations.

4) Stealth difficulty is exactly the same as Extreme difficulty but without the marking (Performance mode) in terms of the markings AND the ripples. Therefore, I highly recommend you to write down the location of each unlocked ripple to remind yourself when your playing on Stealth. Another idea which I haven't done but would work amazingly if timed properly is to have a video record of the song on Extreme your cell phone for example and follow it on Stealth.

5) In the game, the songs are categorized into five difficulties, the more the white marking the more difficult it is. And so, it would be a very smart idea to get as many ripples as you can from the easy ones so you won't have to get as many on the difficult ones. For example, getting 20 ripples on a tier 1 song + 10 on a tier 5 song is much easier than getting 15 from both songs. If you followed this promptly, you will end up getting as low as 1, 5 & even 6 ripples only from certain song like I did.

6) Please note that sometimes at certain songs, a good timing of the parallel universe (PU) could actually reward you with the all the ripples. And at some songs, you'll need to get all perfects at the beginning so you can go into the PU pretty soon to get the first ripple.

Hope this will help, and good luck as this achievement requires patience and persistence

I tried to find any guide/video but the only one is this one (Its in Japanese, so get a translator). All songs in all difficult levels

http://www22.atwiki.jp/danevo/pages/27.html