Dave Grohl performs in concert at the Sound City showcase at Stubbs BBQ during SXSW

Between rehearsals of Chicago with Robin Thicke and a super group that brings together Trent Reznor, Dave Grohl, Lindsey Buckingham and Queens of the Stone Age, the GRAMMYs' consulting sound engineer Doug Mountain took us on a tour of Staples Center and detailed the technology being used for Sunday's telecast.

As of 1 p.m. Friday (Jan. 24), there were up to 50 wireless microphones and 18 wireless guitar set ups -- and both those numbers will grow as each band comes in for rehearsal. The Reznor-Grohl-QOTSA outfit took the stage and spent a good 15 minutes getting the drum and electronics sound correct before rehearsing the song.

They, like all of the 21 scheduled performances, run through the song four times. They then bring in the lights, camera and effects for another four run-throughs.

A voice boomed over the PA -- "Dave wants more shaker" -- after one run-through and as they set about building their two-song medley (GRAMMY organizers want us to keep it a secret), they very loudly applied one layer atop the other. Meanwhile, in other corners of the Staples Center, musicians were rehearsing for the Beatles special that will tape Monday. Among the songs to be covered: “While My Guitar Gently Weeps,” “Let it Be” and, a bit of an obscurity, “Hey Bulldog.”

The rehearsals will continue through Saturday night with the arrival of Madonna and, if time allows, Jay Z and Beyonce, who are not expected until late Saturday night. They might be rehearsing the morning of the show.

Mountain broke down the production by the numbers:

3 million watts of electricity will be used to power the venue and production.

4,000 staff members, but only 3,200 parking spaces.

1,000 video clips loaded for use during the show. About 200 of them will never be used.

230 audio frequencies in use during the show.

192 channels to feed audio signals to multi-track recordings.

170 tons of equipment hanging from the roof of Staples Center

64 JBL Vertec speakers.

21 subwoofers -- 16 in the air with five on the ground to rattle Staples.

17 cameras for the telecast -- three of which are Steadicams.

10 animators to create visual images for the performances.

10 video screens that collectively weight 3 tons.

10 smoke machines

8 tractor trailers of equipment.

5 tons is the weight of P!nk's flying rig alone.

0 pre-recorded lead vocals.