• From: Wien
  • Registered: 2007-05-01
  • Posts: 99

Topic: Measuring used bit depth

I am trying to determine the bit depth of an A/D converter by means of passing the signal through the AES (lightpipe) input of my UFX box and then monitoring it with Digicheck 5.90 in Bit Statistic mode. The trouble is, whatever I measure, using this mode always indicates 24 active bits, even if I play an 8 bit file from Samplitude or Cool Edit Pro 2 and monitor the relevant output channels.

Am I doing something wrong?

David

Classical ambisonic surround recording: UFX, FF400, Alesis HD24, Edirol R-44/88, Samplitude ProX 3.

david-p's Website

2 Reply by MC

  • MC
  • MC
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  • From: Germany/Thailand
  • Registered: 2007-04-06
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Re: Measuring used bit depth

AES has 24 bit. And the output of an ADC is at least 24 bit of noise. Sam and CE most probably dither to full resolution. To play back real 8 bit only you must disable anything within Sam/CE that might tamper the signal.

Regards
Matthias Carstens
RME

MC's Website

3 Reply by david-p (edited by david-p 2017-05-10 11:22:20)

  • From: Wien
  • Registered: 2007-05-01
  • Posts: 99

Re: Measuring used bit depth

Indeed, if I limit the Device Resolution/Driver Communication parameter in Samplitude's preferences to 16 bit, signals are read as such in Digicheck.  But otherwise, it is hard to see what one can actually measure with this function that is useful, and I suppose that the only way I have of measuring the bit depth of my A/D convertor is to input a very low level sine tone and see at what point it becomes a square wave!

David

Classical ambisonic surround recording: UFX, FF400, Alesis HD24, Edirol R-44/88, Samplitude ProX 3.

david-p's Website

  • vinark
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Re: Measuring used bit depth

If it is a 24bit converter, never. It will drown in the noise before that. On a 16 bit recording from a 24 bit AD yes if it is not dithered before truncating.

I am trying to determine the bit depth of an A/D converter.
Well if 24 bits are active it is 24 bit, lol. How useful those 24 bits are is determined by the noise floor and distortion. Real 20 bit would be 120db.

Vincent, Amsterdam
https://soundcloud.com/thesecretworld
BFpro fs, 2X HDSP9652 ADI-8AE, 2X HDSP9632

5 Reply by MC

  • MC
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Re: Measuring used bit depth

I think you (David) try to convert the SNR to bits. That is a misleading and partially wrong method to show (not measure) the relation between dynamics and bit depths. Meters that do so exist, but they make no sense as dither (any kind of noise floor) can vastly improve the resolution beyond any 1 bit = 6 dB formula.

The purpose of the DIGICheck bit statistics is to find the real word length of the current signal, and to see DC parts and bit problems in it.

With an AD converter the 'resolution' that you would like to see could be measured via the signal (0 dBFS) to noise (basic noise floor) ratio. You can read that value limited to the audio band from the same function, by just shortening the ADC's input. Then divide that number by 6 and you get the 'bit depth'...

Regards
Matthias Carstens
RME

MC's Website