Have a look at this superb footage of a launch. The Shuttle main engines start first - to make sure they are all healthy - before the boosters are started. You can see (and hear) the whole STS angle over with the force, and then the boosters are lit.
https://m.youtube.com/watch?v=Lq_shHu4lAs
Another revealing look at a shuttle launch is here:
https://www.youtube.com/watch?v=C0OmJFFQp50
If you look at 5:07, you will see just how violent the ignition of the solid rocket boosters was.
Also extremely interesting is this video, which is part 2 of about 30 minutes of 400 fps video of the launch from various engineering cameras:
https://www.youtube.com/watch?v=M0L5CBrqE2U
Go to 9:20 to see just how rough was the thrust that the SRBs produced; essentially the thrust pulsed about around 7 hz. SRBs were not an elegant technology.