Topic: 32Bit Float recording - The Technical view

[aaronji]

Someone correct me if I'm wrong, but I think Sound Devices had multi-ADC designs even before their products had a 32-bit float option at all.

The first generation MixPres have multiple ADCs, but no 32-bit float. I (accidentally) tested this out once and was able to add more than 30 dB of gain with no audible noise.

The high-end SDs (833/888/Scorpio) also used multiple ADCs without 32-bit float since their release (2019). I think they only implemented 32-bit float via a firmware update last year (May 2024).

[unidentified]

Multi ADCs do allow for a wider dynamic range to be recorded.  But indeed, they don't help with anything before the ADC, except perhaps the designers will couple a dual ADC system with upstream components which can make that wider dynamic range worthwhile.  Well, possibly...

Yeah, or they can implement two crappy cheap analog signal paths feeding two crappy ADC's, combining them with a crappy algorithm and still wave the dual-ADC 32bfp flag to make it sell  .  But indeed, on the bright side: The multi-ADC technology, combined with 32bfp does open up options to further improve recording quality at a reasonable pricing, and fortunately some devices are actually doing this!

I don't recall if the Zoom F3 was the first commercial device to combine dual ADCs, floating 32 bit tech, and super quiet pre-amps for a few hundred dollars, but the ones I own do a great job with no audible artifacts, even when I amplify quiet passages beyond all reasonable limits in post (perhaps to hear a musican whisper the song's title to bandmates).

[Ozpeter]

I've now been told by B&H that the very popular DJI Mic 2 wireless mic that records in 32 bit float is, as I suspected, a single ADC device.  Given that I can't find any 32 bit float recording wireless mic that does claim dual converters, I suspect that all of them are pointlessly writing 24 bit data into a 32 bit float container.

I do feel that this whole "fake" 32 bit float thing is something of an industry scandal.  And I've been posting about it all over the internet  .  I do hope someone here will tell me if in fact there is a worthwhile point in using a single converter to write 32 bit float files, before I embarrass myself further!

[Edited to add that DJI themselves have now confirmed what B&H stated.  They say "DJI Mic 2 32-bit float recording adopts a brand new audio encoding and recording method, which expands the recording range and effectively solves the problem of audio overexposure." Really?  From a single 24 bit ADC?  How?]

[Rairun]

I've now been told by B&H that the very popular DJI Mic 2 wireless mic that records in 32 bit float is, as I suspected, a single ADC device.  Given that I can't find any 32 bit float recording wireless mic that does claim dual converters, I suspect that all of them are pointlessly writing 24 bit data into a 32 bit float container.

I do feel that this whole "fake" 32 bit float thing is something of an industry scandal.  And I've been posting about it all over the internet  .  I do hope someone here will tell me if in fact there is a worthwhile point in using a single converter to write 32 bit float files, before I embarrass myself further!

[Edited to add that DJI themselves have now confirmed what B&H stated.  They say "DJI Mic 2 32-bit float recording adopts a brand new audio encoding and recording method, which expands the recording range and effectively solves the problem of audio overexposure." Really?  From a single 24 bit ADC?  How?]

I can see how using 32-bit float would be simpler there. They do have to make sure that anything under the microphone's maximum SPL doesn't clip digitally as it goes through the 24-bit ADC, BUT after the analogue signal has been converted, they also have to allow the user to set the volume (to feed, for example, a camera) - and sure, they could simply name this volume the "output volume", but maybe they felt this would be confusing and opted for it to be both. So by saving the data to 32-bit float, it allows the user to set whatever volume they want (even if they run the risk of overloading the camera they are feeding), while also avoiding clipping the mic's internal recording digitally.

[Ozpeter]

Devices which write 32 bit float files using only one  ADC (confirmed by manufacturer) -

Zoom H1 essential
Zoom H2 essential
Zoom H4 essential only uses dual ADC on inputs 1 & 2
DJI Mic 2
Tascam DR-07XP
Tascam DR-05XP

Response awaited from Rode regarding the Wireless Mic Pro

Obviously there are loads more devices out there which might write to 32 bit float from single converters, and I may get specific info on some more, but as a rule of thumb, Zoom said that as far as their product range is concerned, if there is no claim in their publicity for the device that it has dual converters, then it doesn't.  I suggest extending that way of assessing devices to all other companies.

I have started a discussion on Reddit about this - simply trying to spread the word, to undo the assumption that 32 bit float means extended dynamic range from multiple ADCs - 15,000 views in 5 hours, plenty of comments - I did say in the first line that the whole subject came up from someone's post here!

[Ozpeter]

The Reddit thread has had 22,000 reads in 11 hours so at least the subject is being kicked around widely.  One response has suggested that 32 bit float from a single ADC can be implemented with clipless dynamic range being enhanced by an entirely different method than dual ADC methods.

"It is possible however to achieve the same result with a single ADC. A dual path preamp can be triggered to change its gain on the analog side if clipping occurs and the DSP could then digitally trim up the digital signal. It's a bit harder to do as you need precise timing adjustment and the analog circuitry needs to be quite precise (maybe even calibrated at manufacturing) but overall it would have the exactly the same performance for far less costs. This is how some digital desk preamps are actually made. Analog gain is stepped and digitally compensated to give the illusion of continuously variable gain."

I think I can follow the meaning of that, just.  It appears to be as if the analog signal is compressed to avoid clipping on the analog side, but then uncompressed once converted to 32 bit float data.  But is that a good idea in terms of the integrity of the audio?  And if it is a good idea, is it just as good as using dual ADCs?  And if it's just as good as using dual ADCs, why isn't it being used in the top flight devices?  And why are the companies not making the thing known, like they were happy to do with endless diagrams in publicity for dual ADC devices?

I suspect I'm getting obsessed with all this...     Sorry!

[adrianb]

I suspect I'm getting obsessed with all this...     Sorry!

You might be obsessed with investigating this and writing about it, but I’m obsessed with reading about it so don’t be sorry.

[WiFiJeff]

Does anyone know if the Tascam FR-AV2 uses two ADCs for the external in (as well as for the XLR in), or is it crippled like the X8 external input?

[dogmusic]

The TASCAM DR-10L PRO uses dual ADC for 32-bit Float recording on its single 3.5mm (1/8") TRS jack.Tascam might have implemented this also on the FR-AV2 3.5mm external input.

[Ozpeter]

The problem with devices which seem not to have dual ADCs on all their inputs, only on some, seems to relate to the inputs being recordable at the same time to multiple tracks.  With devices that can use only one input or the other at the same time, then they only need to provide one pair of ADCs to deal with it - the input will be passed to the same dual ADCs from whichever input it in use.  So, if the Tascam FR-AV2 can only record to one stereo track at once, I can see no reason why its dual ADCs should not be employed on whichever input is used.  But - I don't actually know.  (The Zoom H1 XLR has dual converters and there's nothing in the manual to suggest that the 3.5mm input doesn't go through them - and it is rather cheaper than the FR-AV2!).

[Joop]

I don't know what you all want, but the bottleneck of all is the dynamic range of the ADC. Also double ADC's don't double the dynamic range because they all have the same ground. If not that would be an interesting schematic for studying. The maximum possible dynamic range is the range between ground and the maximum voltage, this is not necessary the same as the total voltage of the batteries,   multiplying is possible, in that case your power usage is going up.

[datbrad]

I don't know what you all want, but the bottleneck of all is the dynamic range of the ADC. Also double ADC's don't double the dynamic range because they all have the same ground. If not that would be an interesting schematic for studying. The maximum possible dynamic range is the range between ground and the maximum voltage, this is not necessary the same as the total voltage of the batteries,   multiplying is possible, in that case your power usage is going up.

tut
I never read anyone claim that dual 24 bit ADCs doubles dynamic range. The idea is to "stretch" the dynamic range of the written file by 8 bits. I think we all know dynamic range is limited to the analog  signal, with the best being about 120 db SNR.

[Gutbucket]

The Reddit thread has had 22,000 reads in 11 hours so at least the subject is being kicked around widely.  One response has suggested that 32 bit float from a single ADC can be implemented with clipless dynamic range being enhanced by an entirely different method than dual ADC methods.

"It is possible however to achieve the same result with a single ADC. A dual path preamp can be triggered to change its gain on the analog side if clipping occurs and the DSP could then digitally trim up the digital signal. It's a bit harder to do as you need precise timing adjustment and the analog circuitry needs to be quite precise (maybe even calibrated at manufacturing) but overall it would have the exactly the same performance for far less costs. This is how some digital desk preamps are actually made. Analog gain is stepped and digitally compensated to give the illusion of continuously variable gain."

I think I can follow the meaning of that, just.  It appears to be as if the analog signal is compressed to avoid clipping on the analog side, but then uncompressed once converted to 32 bit float data.  But is that a good idea in terms of the integrity of the audio?  And if it is a good idea, is it just as good as using dual ADCs?  And if it's just as good as using dual ADCs, why isn't it being used in the top flight devices?  And why are the companies not making the thing known, like they were happy to do with endless diagrams in publicity for dual ADC devices?

What you describe is companding - essentially a form of lossy compression used to increase dynamic range throughput and has been around for a long time. Compress on the way in then expand on the way out by the same amount. Dolby and DBX noise reduction schemes are examples of compansion tuned specifically to improve dynamic range of analog tape, with the more specific goal of noise reduction.   Conceptually, substitute the single ADC for the magnetic tape portion of the signal chain, with the compression being done in the analog circuit path ahead of the ADC, and expansion done digitally afterward.  The trick is getting the two to match identically such that the expansion exactly counters the effect of the compression, and maintaining the required design tolerance in doing so over time.  It's a legitimate work around, but is not free of trade-offs.  No free lunch.

[Gone Fishin']

^^ what he said

Dual-ADC method isn't that difficult and the circuitry costs not that expensive.
At this point in the evolution of the technologies, it seems the way to go.

Will that be bested?
Probably
But modifying analog stages just seems like a step backwards, and more likely to introduce artifacts which cannot be undone.

[Billy Mumphrey]

Solution: a compact field recorder that accepts AES42 (digital microphone) signals. No more 32FP! ))