Guitar Hero: Warriors of Rock

I got this by myself in local QP+ using 1 mic and my headset (signed in on an offline account) as the other mic (and two controllers) and no other instruments. so I'm guessing you only need 2 people to get this not 4 people like some other achievo's . I don't know whether this works over live though.

Edit : This does work over live. Thanks to Spilner1001 for confirming that.
Also can be definitely be done with only 2 people. Thanks to DJP519 for backing me up with that one.

Edit2 : "Another thing to note, I just had a MM session for this achievement. Had 2 vocalists on Medium and 2 bassists (one on expert and one on hard). Achievement didn't pop.
Then both the bassists dropped to medium and then the achievement popped. All these players were on separate consoles over xbox live."
Thanks to Flopsy86

There is an easy way to unlock this achievement and you don't even need to sing, just play a video of someone else who can sing into the mics.

- Create a quickplay match with 2 players on medium (your profile and a guest) with two controllers and two headsets
- place the mic close and remove the little sponge, now put them between the earphones and try to synchronize the video and the game... just be sure you don't fail the song
-at the end of the song you have your easy 10G

Confirmed by TBonePhone: Used USB Mic and a headset placed next to a speaker, worked perfectly first try.

I've got this one on my first try using the video linked below

Here's a solo solution for people that have an aversion to singing. This achievement only requires 2 players, unlike the other achievements that explicitly state a need for 4 players.

You need:
-Two controllers
-Two microphones (standard USB mic or headset both work)

Go into Quickplay+ and make sure your main account and second/guest account are both set to Medium. Continue through the setup process and then start the song. As soon as it loads, hit Start and go to Options > Audio Mixer. Turn everything down as far as possible except Vocals, which you want to turn up. Put both mics up to your speaker, turn the sound up a bit, and then play the song. No need to sync to an online video!

You won't keep a streak, but it's good enough to complete the song.