Quick way to find the latency of a device?

[daniel]

Is there a way of finding the latency between the analogue ins and outs of a digital device, in the field without bringing the files into a computer?

I was wondering if sending a tone sweep through an analogue mixer, through the digital device and back to another I/P on the mixer would indicate the delay by what frequencies get louder and get attenuated? Eg. If the summed signals dip at 125hz (8ms wavelength) the delay would be 4ms, which should mean the signal is doubled with a tone at 250hz? 

[rich]

you can test it if you are able to plug into a unit that accepts digital and analogue ins and has adjustable input delays and a phase reverse.

plug the analogue and digital outs into the above mentioned recorder, flip the phase on one input, send tone or any signal from the machine you are looking to test, 

set the gains on the second recorder so that both inputs are equal level, fade them up equally, the adjust input delay on whichever channel you think will have the least latency until you get the most cancellation.

bear in mind though that AtoD and DtoA will affect latency. though if you are lucky, the designer of your machine will have considered this and compensated.

and hopefully, there is not a change in latency at the machine you are using to measure this.