<p>I was reading the paper about the first M87 EHT Results, part 3 (<a href="https://arxiv.org/pdf/1906.11240" rel="nofollow noreferrer">link to article PDF</a>), where the data processing pipeline is explained. The recording system used was a Mark 6 recorder with 32Gbps and 2 bit sampling. Why is the quantization so coarse? I think I am missing something since the measurements have a very large dynamic range. Can anyone explain what this 2 bit sampling means?</p>

CC BY-SA 4.0
2022-10-10T20:39:25.357Z
Sounds like it 4-level (2 bits) of quantization sampled at 16 gigasamples per second (32 Gbps / 2 bits per samples).   High speed analog to digital converters usually have a coarse resolution.  I don't have a reference to the design, or I'd use this as part of an answer.
GrapefruitIsAwesome
CC BY-SA 4.0
2022-10-10T22:37:26.027Z
[Homepage](https://www.haystack.mit.edu/mark-6-vlbi-data-system/) for Mark 6 VLBI data recording system - may be too far down into the hardware/computing weeds...
astrosnapper
CC BY-SA 4.0
2022-10-10T22:57:42.617Z
Different but related: [Why are the ALMA receivers' ADCs only 3-bits?](https://astronomy.stackexchange.com/q/18052/7982) There are four answer posts there, but I still don't really understand why. I assume that there is mathematical magic that shows that for some bandwidth limit one can recover the full signal by oversampling in speed while under-sampling in resolution, but I don't know what that is yet. I'm sure that's the easier option for the hardware designer; nobody want's to make a 24-bit 2 GHz ADC with ultra-low differential nonlinearity if they don't have to.
uhoh
<event-horizon-telescope><vlbi>
Mark 6 VLBI Recorder 32Gpbs, 2 bit sampling
acoustica
# Mark 6 VLBI Recorder 32Gpbs, 2 bit sampling

(Asked by: username_0 on 2022-10-10)

I was reading the paper about the first M87 EHT Results, part 3 ([link to article PDF](https://arxiv.org/pdf/1906.11240)), where the data processing pipeline is explained. The recording system used was a Mark 6 recorder with 32Gbps and 2 bit sampling. Why is the quantization so coarse? I think I am missing something since the measurements have a very large dynamic range. Can anyone explain what this 2 bit sampling means?

**Tags:** event-horizon-telescope, vlbi
> **Comments:**
> **username_1**: Sounds like it 4-level (2 bits) of quantization sampled at 16 gigasamples per second (32 Gbps / 2 bits per samples).   High speed analog to digital converters usually have a coarse resolution.  I don't have a reference to the design, or I'd use this as part of an answer.  
> **username_2**: [Homepage](https://www.haystack.mit.edu/mark-6-vlbi-data-system/) for Mark 6 VLBI data recording system - may be too far down into the hardware/computing weeds...  
> **username_3**: Different but related: [Why are the ALMA receivers' ADCs only 3-bits?](https://astronomy.stackexchange.com/q/18052/7982) There are four answer posts there, but I still don't really understand why. I assume that there is mathematical magic that shows that for some bandwidth limit one can recover the full signal by oversampling in speed while under-sampling in resolution, but I don't know what that is yet. I'm sure that's the easier option for the hardware designer; nobody want's to make a 24-bit 2 GHz ADC with ultra-low differential nonlinearity if they don't have to.  

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## 0 answers

