Re: Driving a USB device at 32 bits per sample
Re: Driving a USB device at 32 bits per sample
- Subject: Re: Driving a USB device at 32 bits per sample
- From: Paul Davis <email@hidden>
- Date: Wed, 04 Apr 2018 08:38:02 -0400
Lets differentiate between a couple of things:
1) 32 bits used to transfer the sample value between the audio interface
and the CPU
2) the analog-to-digital converter generating 32 bits of information for
each sample value
The first one is relatively common - there are many interfaces that do
this. They pack 24 bits of sample value into a 32 bit unit, aligned either
LSB or MSB, and occasionally (hello, RME!) use the other 8 bits for
carrying other information (e.g. timecode)
The second one is completely absurd. 32 bits of information means that the
least significant bits are determined by atomic brownian motion. Not only
is it not possible that the converter is measuring this, even if it could
you wouldn't be interested. Most 24 bit converters have a hard time
actually getting to full 24 bit resolution, so the idea that you can go 7
or 8 orders of magnitude beyond that (each extra bit doubles the
resolution) is absurd unless you're doing science.
So, which situation are you actually dealing with, and are you clear on how
absurd 32 bits of "value" per sample is?
On Wed, Apr 4, 2018 at 6:39 AM, Paul Sanders <email@hidden>
wrote:
> Hello again,
>
> Same person, different question.
>
> I have a USB ADC here that can do upto 32 bits per sample and indeed it
> shows up as such when you ask it what it can do, but if you ask Core Audio
> to record at 32 bits then it still tells the device to operate at 24 bits.
> Is this intentional and is there anything that can be done about it?
>
> I have a legitimate reason for asking but it is commercially sensitive so
> I won't share it here. I am talking to the device through AUHal but I
> don't think that's relevant. Tested on Sierra 10.12.6
>
> Screenshot from Audio MIDI Setup here: http://www.alpinesoft.co.uk/pr
> ivate/audio_midi_setup_screenshot.png
>
> TIA - Paul Sanders.
>
>
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