I've seen a "synthesiser" or "synth" mode a few times on various high-spec function generators and I can't seem to quite get a clear answer.

What does it do and what are some example uses?

Thanks

 

My guess would be: To synthesize a specific waveform - like a staircase wave form where one can define each step size and duration.

 

link

A frequency synthesizer is an electronic circuit that generates a range of frequencies from a single reference frequency. Frequency synthesizers are used in many modern devices such as radio receivers, televisions, mobile telephones, radiotelephones, walkie-talkies, CB radios, cable television converter boxes satellite receivers, and GPS systems. A frequency synthesizer may use the techniques of frequency multiplication, frequency division, direct digital synthesis, frequency mixing, and phase-locked loops to generate its frequencies. The stability and accuracy of the frequency synthesizer's output are related to the stability and accuracy of its reference frequency input. Consequently, synthesizers use stable and accurate reference frequencies, such as those provided by crystal oscillators.

I have some generators that have one oscillator and it runs at the output frequency. I have other generators that use a 10mhz reference and divide and multiply to get the output.

 

I've seen a "synthesiser" or "synth" mode a few times on various high-spec function generators and I can't seem to quite get a clear answer.

What does it do and what are some example uses?

Thanks

More correctly they are AWG's, Arbitrary Waveform Generators.
You can do all manner of things with one like trigger their 2nd channel from the first with timed pulses and the like as you can do with glue logic. That's a very simple example as some of their capabilities are quite complex just using the UI but if programmed most anything you can imagine is possible. Waveform parameters are run or installed into memory where the better units have deep memory to allow for this.
Great for testing circuits during development or the cheaper ones make a great scope learning tool.
All serious hobbyists should have an AWG.