• RobHu
  • ADAT user
  • Offline
  • Registered: 2017-01-03
  • Posts: 22

Topic: 24-bit limitation on MacOS?

I have just done the bit test with my ADI-2 Pro, and while the 24 bit test passes the 32 bit one does not.

The manual says "Mac OS X, iOS, AES and SPDIF are limited to 24 bit.", and indeed Audio MIDI Setup for ADI-2 Pro it says "Format: 44,100 Hz 2 ch 24-bit Integer".

Could you please tell me why it is that Mac OS is limited to 24 bit, and whether I am "missing" fidelity I could conceivably have with the ADI-2 Pro if I were at 32 bit (perhaps with Windows?)

Thank you.

2 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

You don't miss any fidelity with 24 bits. Because you have no source that would exceed that dynamic and THD range. Not to mention that real-world DACs do not reach those limits either.

Mac/iOS Core Audio performs a conversion from 32 bits integer to floating point. The floating point resolution is 24 bits integer with 8 bits mantisse, which is not able to represent a full 32 bit integer resolution unchanged. Therefore you get full 24 bit resolution only.

The reason the Audio MIDI Setup shows 24 bit is a different one, the CC hardware signals that. We will change that to 32 bits, but it will not change the effective, real resolution. You most probably then get 32 bits integer as playback format shown, but still can not exceed the 24 bit accuracy as proven via Bit Test.

Regards
Matthias Carstens
RME

MC's Website

  • RobHu
  • ADAT user
  • Offline
  • Registered: 2017-01-03
  • Posts: 22

Re: 24-bit limitation on MacOS?

Thank you.

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

Why 32bit not passed even when using Audirvana or JRiver with integer mode?

5 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

You read post number 2, paragraph 2?

Regards
Matthias Carstens
RME

MC's Website

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

Yes, I read.

An explanation of Integer mode is here.
http://www.amr-audio.co.uk/large_image/ … 20Mode.pdf

There is written like this.
"In Integer Mode (see figure 3) the player software supply a stream already formatted in the native DAC format, ..."

Is Integer mode not able to bypass the floating point?

7 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

The answer is there as well:

>This is only applicable to compatible DACs  that offer this non-standard mode.<

Means a special driver is needed. But the ADI-2 Pro and DAC are Class Compliant devices (like most DACs) that do not use a driver under Mac OS X (like most DACs).

Regards
Matthias Carstens
RME

MC's Website

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

No special driver should be needed.

Audirvana Plus rev. 3.1.8 (3128) debug information:

Audio settings:
    Hog Mode: on
    Direct Mode: off
    Integer Mode: on    Mode 1
    Max Mem for audio buffers: 13312MB
    Max Sample rate limit: None
    Sample rate switching latency: None

CoreAudio audio path, buffer I/O frame size: 512

Preferred device: ADI-2 Pro (XXXXXXXX)    Model UID:ADI-2 Pro (XXXXXXXX):2A39:3FD2    UID:AppleUSBAudioEngine:RME:ADI-2 Pro (XXXXXXXX):XXXXXXXXXXXXXXX:1,2

Currently playing in Integer Mode:
    Device: 2ch Non-mixable linear PCM Interleaved 32bits little endian Signed Integer, 8 bytes per frame 44.1kHz

9 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

@ takt: I don't understand what is going on here. If you already know that the ADI-2 Pro works like that in Audirvana with special settings what are your posts good for then?

Regards
Matthias Carstens
RME

MC's Website

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

I think
Integer mode does not include processing of floating point.
Integer mode should be able to play 32bit.
But even with integer mode, Bit Test is not 32bit passed.
Why?  Where is the cause?

11 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

You better ask the developer of that mode then. The ADI does pass 32 bit with ASIO drivers under Windows, which confirms that 32 bit data can be transferred to the unit correctly.

Regards
Matthias Carstens
RME

MC's Website

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

Does ADI-2 Pro do the same 32bit processing for both ASIO and Class Compliant?

13 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

Yes. Data transfer from/to the computer is identical. We only added flow control for ASIO.

Regards
Matthias Carstens
RME

MC's Website

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

Thank you for your response.

15 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,582

Re: 24-bit limitation on MacOS?

Epilog: I was not aware that some audio players offer a special mode to transfer 32 bit integer data on Mac OS X. I was aware of the format as such (non-mixable), but not that Core Audio can use it with Class Compliant devices like our ADI-2 Pro and ADI-2 DAC. That's a nice surprise!

As mentioned we do transfer all 32 bit unchanged in any way under whatever OS, and the bit test works even with 32 bit under Mac OS X when using HQPlayer 3.20 (trial version is sufficient to verify). Audirvana and JRiver do not pass the test at this time.

Regards
Matthias Carstens
RME

MC's Website

  • takt
  • ADAT user
  • Offline
  • Registered: 2017-12-16
  • Posts: 8

Re: 24-bit limitation on MacOS?

Thank you.  That's good infomation.
I confirmed "32 Bit passed" is displayed if using HQPlayer Desktop version 3.20.0.