The Freeze function of Ableton’s Ping Pong delay is something that I didn’t discover until late in the game. It is easy to miss because it is a tiny button on the interface; just an inconspicuous button marked “F” to the right of the “Sync” button. But what it does is pretty cool and now I am totally addicted.
Unlike the normal functioning of the delay, which constantly refreshes the signal being delayed, the Freeze button ignores any new incoming signal and just repeats the delayed signal until the Freeze button is turned off.
Functionally, this is very similar to a Beat Repeat function because it can be used to make a stuttery effect. Key or MIDI mapping the Freeze button will allow you to grab a little piece of audio on the fly and repeat it until you release the button.
I really only have two complaints about the freeze function, and they’re small ones.
For some reason, the Freeze button is a toggle. This means that you actually have to depress it twice, once to turn it on and once to turn it off. This is rather inconvenient in a live setting.
Also, for some reason, the Freeze parameter doesn’t show up in the envelope automation. This means you can’t automate it, which is a bummer. Both of these problems are pretty easily solved, though, by assigning this button to a Macro.
Even though most people only use Macros when they make an effect or instrument rack with more than one device, there’s no reason why you can’t make an effects rack with just one Effect.
Just select the effect that you would like to make into a rack (Ping Pong delay in this case) and press Cmd+G.

Now, press Map Mode in the Macro panel and assign the Freeze button to a Macro.
But Anthony, you say, why would I assign a button to knob?
Glad you asked.
This will allow you to do two things. You can now automate the freeze effect using envelopes (as I did in my generative music Live Pack). You can also now map the knob to a momentary Midi button. Most MIDI controllers will have an option to change the functioning of certain buttons from Momentary to Toggle and vice versa. Simply MIDI map the Freeze macro knob to one of these buttons and you’ll be able to use the freeze effect on the fly. I usually map the Wet/Dry knob to the same Macro, so that I can turn it up very high instantaneously, effectively cutting off the non-effected signal. This functions as a full beat repeat.

I hope you find this helpful! Let me know in the comments, on the Facebook or on Twitter if you have any questions.