Hi,
Looking on the website I didn’t find any considerable difference between the two, do they use different chips for ADC?
I checked the datasheets on the website and found some differences. The PRO version has the following in addition:
- Low-jitter dual-domain clock for optimised clock decoupling from the Raspberry Pi
- Mic bias voltage for the use with electret microphones
- No anti-aliasing filter in the input path for best recording bandwidth
The first item is the most relevant difference I would say, the second item depends on whether you need this. I would not worry that much about the third point - a properly designed anti-aliasing filter should be totally fine (and the chip will have one internally anyhow).
// EDIT:
Here, an official link discussiong the clock and jitter
More fundamental explanation of the effect and what it means
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You asked specifically about latency. Overall latency is no affected by the clock as such. The sample rate and buffer quantity / size are the defining parameters plus some small but mostly insignificant electronic latency. A better clock improves jitter which is the variation in latency but that effects the sound rather than any perceived latency because it is orders of magnitude smaller than the latency, e.g. Zynthian may have a latency of 11ms and jitter of +/- 10us which could increase latency to 11.01ms. I challenge anyone to observe that difference without an oscilloscope 
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In this case the ADC DAC audio processing, both would have the same latency, correct? Would the difference be in the fidelity of the frequencies captured?
Yes, the input and output buffers are the same size, being processed at the same rate.
If there is jitter on the clock then there is a variation it the sample rate having an impact on the audio, a bit like phasing but not as evident. In fact most people wouldn’t notice the effect and those who do probably couldn’t identify how the audio was effected. They may have a preference for one or other but not necessarily the lower jitter.
Although in general we want to minimise temporal jitter, there is an effective tool to add jitter to sample data in order to mask quantisation noise. This may not be pertinent to this discussion on clock jitter but worth mentioning so that we avoid confusion which otherwise may lead someone to avoid good jitter.
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Interestingly, I’m building a Frankstein with an old keyboard with a burnt motherboard, I’m using the keys with an Arduino Mega and I’m going to use the zynthian as the keyboard’s “brain”. As it has several engines and among them there is the possibility of external audio processing, I want to use an interface with ADC. Looking at other posts I saw that on cards that go directly to Raspberry’s gpio latency is lower than on USB interfaces.
My concern was with latency, I believe HIFIBERRY DAC+ ADC will serve me 
Thank you very much for the clarifications @riban and @0penSourceFreedom !
That sounds like a very interesting project! There is a thread with “Success Cases” - feel free to add your version when you have put something together and running 
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