They are two different detections. I wouldn't put much faith in what the Chinese detected, as they were just hand held ones that they where holding over the edge of the ship, so they could have been causing interference. So i think they have already been discredited. The important one is the one being towed under the US or Australian ship. It also has an echo, which is consistent with a flight recorders, as that has two pings where one of them would be like an echo. I think that it is highly likely it is from the plane, because it can't really be created by anything else. But even knowing the broad area, it will be like finding a needle in a haystack when they get down there.
The FDR and/or CVR do not provide an echo type signal. They are two separate units each with their own pinger. Hence two signals. They might sound like an echo but are two very separate signals.
Yes that is what I meant. This is why if they only heard a single ping every second, instead of two pings (one sounding like an echo) then it would be unlikely they heard the flight recorder. I believe the chinese one was just a single ping every second, and only for a short duration, which is another reason why that wasn't very credible.