Impact of interest rates on value of risky bonds

[afterworkguinness]

Hi,
Can you expand a bit further on these relationships laid out in the notes on Stulz ? Thanks

Increase in the positive correlation between firm value and interest rate shocks (what shocks ?) causes a decrease in debt value.

Increase in rate volatility and decimal level of interest rates (what does decimal level mean ?) causes a decrease in debt value.

Thanks