As root under xterm, try this:

1 root@glamb-n900 [~]# cat /sys/power/vdd1_opps_vsel

In my case, it returns:

0 15 26 36 40 42 47 48 50 53 56 59 63 64 68

These are the voltage increase multipliers for all the defined frequencies:

Off 125 250 500 550 600 700 750 800 850 900 950 1000 1100 1200

So in this case, you'll want to increase the 10th value. In my case, it's 53, so bumping that to 55 would probably solve the problem. To do that temporarily:

echo 0 15 26 36 40 42 47 48 50 55 56 59 63 64 68 > /sys/power/vdd1_opps_vsel

To make it permanent, edit /etc/default/kernel-load, and update the line:

VDD1_OPPS_VSEL="0 15 26 36 40 42 47 48 50 53 56 59 63 64 68"

That should do it.

Note though that the processor may be downclocking for short periods while doing DSP related stuff (playing/recording video), and it may be at these voltages the DSP is crashing. So you may have to increase various voltages to get it stable. It takes some patience.

The DSP_OPPS_RATE variable in kernel-load species the frequencies of the DSPs across the CPU freq spectrum in the same way as VDD1_OPPS_VSEL specifies the voltage multipliers, so you can tune the DSP frequencies as well.

To test stability at a given frequency, you could lock the min and max scaling frequencies to the one you're interested in (250, 500, 850, whatever) for short periods to test.