From Friedemann (Ableton) in an old thread (in a now closed Live Beta forum):
the CPU meter in Live works differently than the usual CPU meters in the operating system.
In Live you see the ratio of the time that was actually needed to compute the audio signal and the time that
is available to compute it. The latter is just determined by the sample rate of the audio interface, i.e. at 48kHz
sample rate you need to compute 48000 samples in one second, if it takes longer, there will be drop-outs.
Therefore, values below 100% mean that the samples were faster calculated
than needed by the audio interface while values above 100% mean that calculating the samples took too long
for being delivered to the audio interface on time. In the multi-processor-case the slowest path, i.e. the processor that has to calculate most, determines that number.
On the OS level you usually see how much time a certain processor (or all together) devotes to a certain process.
Although both meters show '%' values, they are not really comparable.