Lips

This requires you to keep the same pitch as the song. You need to try to keep the pitch and fill the singing bars at least 80% of the song to earn the pitch medal.
Practice
Practice
Practice

For this achievement you need to obtain a "Pitch" medal while playing; "Erasure - A Little Respect".

You can obtain said medal and unlock the achievement in any game mode that awards medals, be it single player, duet mode or any other for that matter, if you're awarded the medal you'll unlock the achievement. If you're playing a mode with 2 microphones then it must be the microphone assigned to your account that is awarded the medal, if not you will not unlock the achievement as you didn't earn the medal.

To be awarded a pitch medal you must accurately sing in pitch for an extended amount of time, the longer you do this the more likely you are to unlock the achievement. Unfortunately there's no "easy" way of getting this achievement, the best advice I can give is to keep practicing, it's not the hardest song in the game and after a few attempts you should be familiar enough with the song to unlock this achievement.

Finally, a lot of users try to hold microphones up their TV's, personally I never had any luck with this method and so I cannot vouch for it. However in cases like this I've always found that laptop/desktop speakers are far more effective and so I've linked in the song below. Use it at your discretion, whether trying to familiarise yourself with the song or trying to use it to unlock the achievement. Good luck!

* ^{Credit to EMI Music for the video}