• Registered: 2022-04-23
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Topic: Another Bit Test Question

Was reading the manual on this and it mentions that it can detect hanging or twisted bits. 

If I were to guess I would say that hanging bit is a bit that is stuck at a value and that twisted bits are bits that are alternating in value.

Does anyone know what is meant by these two terms?

2 Reply by ramses (edited by ramses 2023-02-09 19:04:25)

  • ramses
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Re: Another Bit Test Question

It's an end-to-end test from player up to shortly before the D/A converter in the ADI-2 DAC/Pro.

If this fix (predetermined) test pattern is still intact at the DAC, then the transmission of data was without any issues. By this you can validate that your audio has been transferred lossless, which is important when listening to lossless audio (FLAC, ..).

Details see manual ch "Bit test" or
in my blog: https://www.tonstudio-forum.de/blog/Ent … es-EN-DE/.

There is not something like a hanging bit .. what should this be ...?!

Digital audio information is being instantly transferred between PC and Recording Interface/Converter.

Either transport is well or not (cable, plug problem or out of specs, too long, etc) or
audio arrives too late (bad other drivers blocking your computers CPU for too long -> DPC latencies)
or simply performance issues, too high load on the PC or too few cores, etc etc.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13

3 Reply by MatrixS2000 (edited by MatrixS2000 2023-02-09 22:21:35)

  • Registered: 2022-04-23
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Re: Another Bit Test Question

Hi Ramses, I know what the bit test does.

What I don't know is what the terms hanging and twisted bits mean.

From the manual:

"Most bit tests take some time and are loud and unpleasant when playing through headphones or speakers. RME uses a unique bit pattern, with defined levels and pauses. This consists of only 400 samples (<10 ms), and sounds like a dull, medium-loud click - harmless for ears and equipment. The short, but efficient test sequence allows to check for the following changes and errors:

Level changes, equalization, dynamic processing, polarity, channel swapping, sample offset, hanging or twisted bits, dither, bit reduction."

The bolded terms are what I am trying to understand.

4 Reply by KaiS (edited by KaiS 2023-02-10 08:23:08)

  • KaiS
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Re: Another Bit Test Question

Regarding “damaged” Bits:

Bits are transferred as changes between two defined voltages, e.g. like +0.4V for Hi and +0.1V for Low.
To do this, a cable’s capacitance must be charged and discharged back and forth, which takes some time for each Bit, the more the longer a cable is.

Imagine a transfer path like an SPDIF coax cable that’s just slightly too long.

Now most of the time each Bit change between Hi to Low, just so, reaches the trigger voltages before the next Bit is to be send.
From time to time, due to noise e.g., this does not happen, a bit change is lost, the Bit “hangs” or is “twisted”, basically the same thing.

This degrades signal quality, or results in audible clicks.


Practically most data on external cables or through the air aren’t sent as single Bits, but as packets with some error correction, often even with the option to re-send defective packets.

But for SPDIF Optical and Coax, and AES digital this is not the case - what’s lost is lost and causes signal degradation.


To have a simple tool - RME BitTest - to detect this (and other less significant signal changes) is a great achievement.
To my knowledge no other DAC offers this.

KaiS's Website

5 Reply by MatrixS2000 (edited by MatrixS2000 2023-02-10 15:39:53)

  • Registered: 2022-04-23
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Re: Another Bit Test Question

KaiS wrote:

To have a simple tool - RME BitTest - to detect this (and other less significant signal changes) is a great achievement.
To my knowledge no other DAC offers this.

Hi KaiS

Completely agree!  This was one of the factors into my buying decision.

Here is my playback path:

NAS---network switch---network switch---mac mini---ADI

Bit test has given me a tool to test this entire path.  I am glad to report it is clean @ 24/192. 

So back to the my question around hanging and twisted bits, if I understand you correctly, hanging and twisted bits are errors of transitions that were expected but not detected because the transmission technology did not have error correction (unlike ethernet for example).

6 Reply by KaiS (edited by KaiS 2023-02-10 16:52:28)

  • KaiS
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Re: Another Bit Test Question

MatrixS2000 wrote:

So back to the my question around hanging and twisted bits, if I understand you correctly, hanging and twisted bits are errors of transitions that were expected but not detected because the transmission technology did not have error correction (unlike ethernet for example).

Exactly.

BTW:
AES digital and SPDIF Optical and Coax have a parity bit (#31) for error detection, but erroneous blocks cannot not be re-send.
https://en.wikipedia.org/wiki/AES3

KaiS's Website

  • Registered: 2022-04-23
  • Posts: 37

Re: Another Bit Test Question

Thanks KaiS.