Below is the rising edge of a 10 us pulse, configured with 10ns rise time, at 1kHz and at 1Hz. Looks OK.
The third one however is at 100mHz, at the "fastest" setting allowed (90ns rise, 100 us width)). Not exactly "high fidelity"....
DG1032z
And the settings follow that pattern going to longer periods. At 1uHz, the shortest pulse is 10s and the rise time is 9 ms.