Quote from: Jon Stoppable on September 24, 2014, 11:24:37 PM
This depends on the operating level of the recorder, and specifically how they decide to handle the analog input stage. Realize that nearly every ADC chip has a maximum input of about 1VRMS, which is 0dBV (+2dBu). So to interface with 'pro' levels, the input has to be padded before the ADC. Or, if the input level control of the device allows, the sensitivity of the input can be set to any operating level.
tinybox is basically a -10dBV device with a bit of extra headroom (+13dBV). Its noise performance is maximized a little above 20dB gain, so the noise performance is a little worse at +18dB, but for a loud source this just really doesn't matter. If a quiet source is being recorded, I'd recommend using high (+32dB) gain as required.
The DR-680 is probably structured like a 'pro' device, so you need 12dB more gain to hit the same level at the ADC as a recorder that only operates at the 0dBV max level of the ADC. That probably means that even at its nominal 0dB setting, the DR-680 is actually padding the input to the ADC.
A typical condenser mic is around -40dBV/Pa, so a not-very-loud concert will have average level of that, but peak level of up to -20dBV. Given that the maximum peak input of an ADC chip is 0dBV, you shouldn't need more than 20dB gain. There are reasons to use a higher operating level for signal transmission, but in a typical taper situation they wouldn't really apply.
This is why I designed tinybox as a -10dBV device: it is structured exactly to the task at hand, which is recording concerts using condenser microphones into recorders operating at -10dBV. This saves quite a lot of power over the 'pro' level approach of using more gain and a higher operating level, only to pad that level at the ADC. Every 6dB increase in operating level doubles power consumption, so a 'pro' level input will use four times the power of a 'consumer' level input.
Jon I believe you are correct. When I first started using my DR680 I ran the external preamps & therefore the recording levels quite low as everyone had suggested (-16db on the horrible display, with peaks slightly higher) but I found the recordings flat & lifeless even with a healthy bump in post gain as everyone has suggested. It wasn't until I started to run my preamps at higher gain settings that I found the recordings sounding as I had expected. My point is that yes, I believe you are correct in the assumption of the DR680 requiring higher gain levels more than likely due to operating at pro specs, ie padding the input to the ADC. As always your input is appreciated & an asset to the community, thanks.