It's the question that bugs every guitarist each time they pick up their axe - how do I write the next 'Smoke On The Water' or 'Purple Haze'?
John Wheatcroft, Head Of Instruments at prestigious London music school
Guitar X reckons for a start you need to have a time machine...
A recent poll of Guitar X students, carried out in celebration of the school's 25th anniversary, revealed their choice of the Top 25 Greatest Riffs ever - and with only a few exceptions the riffs were all written over 20 years ago.
"Most of our 'classic' riffs are more than 20 years old, with many of them dating back to the late 60s or early 70s," he says. "Artists such as The Beatles, Jimi Hendrix or Led Zeppelin shift just as many albums today, if not more, than they did in their heyday. It's possible that you have to wait until the dust settles to truly consider a riff's eligibility for 'classic' status."
How do you go about creating a classic riff though?
"It isn't as easy as it seems!" says John. "It needs to be memorable, vaguely familiar, able to withstand countless repetition and, most importantly, somehow original."
Not an easy task.
"The one thing that ties all of our classic riffs together is that once you've figured out how to play one on your instrument, you'll wonder why you thought it'd be so difficult to write one yourself."
The students choice of the Top 25 Greatest Guitar Riffs ever are:
1. Smoke On The Water - Deep Purple (1973)
2. Smells Like Teen Spirit - Nirvana (1991)
3. Walk This Way - Aerosmith (1975)
4. Purple Haze - Jimi Hendrix (1967)
5. Sweet Child O Mine - Guns N Roses (1987)
6. Paradise City - Guns N Roses (1987)
7. Ace Of Spades - Motorhead (1980)
8. Enter Sandman - Metallica (1991)
9. Under The Bridge - Red Hot Chilli Peppers (1992)
10. Welcome To The Jungle - Guns N Roses (1987)
11. Run To The Hills - Iron Maiden (1982)
12. Walk - Pantera (1992)
13. Johnny Be Goode - Chuck Berry (1958)
14. Back In Black - AC/DC (1980)
15. Immigrant Song - Led Zeppelin (1970)
16. Wake Up - Rage Against The Machine (1992)
17. Highway to Hell - AC/DC (1979)
18. My Generation - The Who (1965)
19. 7 Nation Army - The White Stripes (2003)
20. Born To Be Wild - Steppenwolf (1968)
21. Give It Away - Red Hot Chilli Peppers (1991)
22. Paranoid - Black Sabbath (1970)
23. Voodoo Chile (Slight Return) - Jimi Hendrix (1967)
24. Eye Of The Tiger - Survivor (1982)
25. Money For Nothing - Dire Straits (1984)