app is inconsistent for me. they say it does a bunch of things like prevent input overload, etc. with level-adjusting apps like voicerecorderpro and metarecorder it seems to be overridden functionally
i open it up to make sure it sees both mics and the HPF is off, levels are ganged approriately (stereo vs dual) then close it and use apogee metarecorder to adjust levels.
its kinda frustrating that support cant explain exactly how it works, if there is a unity gain, and the best settings to set levels. they must have farmed out both hardware and software on this one.
it took a week or so to get an answer from TPTB on whether the d:vice is synchronous, adaptive, or asynchronous. I got this answer and told them to ask again just in case there was a typo or something lost in translation. was hoping the class II operation was asynchronous or at least adaptive. i have heard a click now and again in some recordings but hard to tell if that was just some room noise or something else, not necessarily clock adjusting
The answer from our tech team is;
By connection to PC USB Audio class I is used, in synchronous mode
By connection to Iphone USB Audio class II is used, in synchronous mode
a little background on USB audio from Cambridge
Synchronous USB DAC is the lowest quality of the three often used in low end products, so none of ours course! (that’s right, we’re being smug!) These accept the packets of data whenever the data sends them causing glitches every few seconds due to the differences between the two clocks.
Adaptive is where the DAC constantly adjusts its clock so that it can accept the data being sent from the computer whenever it sends them. The constant adapting of the DAC’s clock means that there is no continuous, accurate master clock in the DAC, which causes jitter in the audio stream.
In both of the above the computer dictates the timing of the data packets being sent.
Asynchronous – this is the most complex to implement but it is a huge improvement on the other types. This is because it requests the data packets to be sent in time with its own clock’s timing, thus providing the lowest jitter and sounding by far the best.
Is jitter in this setup something to be concerned about? hard to say. The effect of jitter seems to be a function of your playback setup as well.
From John Siau (Benchmark), answering in response to feeding DAC1 class 1 usb and also a discussion of playback jitter reduction (emphasis mine):
Up until Windows 7, asynchronous USB interfaces offered no advantages other than a possible reduction in jitter for DACs that lacked proper jitter attenuation. The Benchmark DACs have excellent jitter attenuation, and the asynchronous interface offered absolutely no improvement in jitter performance. The jitter rejection is nearly perfect in both cases.
The V-link will work well if it passes 24-bit audio, and supports the sample rates you are playing. Jitter is never a concern with any Benchmark converter and this means that the v-link's relatively poor-quality synthesized clock will not be an issue.
Doug Oade (again emphasis mine):
The fact jitter will be at unacceptable levels simply demands you use a DAC with an async USB input. That will reduce jitter to the DAC clock's jitter. S/PDIF, which is supported by the controller, has a more stable clock easing the requirements of the DAC. But even a very stable S/PDIF clock in a portable ADC can be improved by reclocking. I use an Apogee Big Ben for that, when needed, in my studio but a high end DAC with an async USB input outperforms the Big Ben. All high end DAC manufacturers now offer async USB inputs with femtosecond accurate clocks. The difference is easy to hear.
i have a tenuous understanding of the effects of jitter, but if you have jitter in the input portion of the recording, how is this clock jitter not a permanent artifact of the recording. in other words, if the data is written 'wrong', how can it be 'read right' later?
and if sound is so dependent on the playback device (which most people in the world are listening on low end equipment, phones, car stereos, computers with dubious interfaces, integrated devices, etc), would it be wise to "clean your clock" by feeding it through a high-end dac>balanced interconnects>high-end low-jitter ADC like an AD2K etc.