Topic: 32Bit Float recording - The Technical view

[dallman]

This started as a recording thread but that has been moved to a new thread, and I leave this for those that wish to debate defend complain or whatever about their gear or the 32bit float process.


I thought with a few new decks having 32bit float recording and more coming, it might be nice to have a thread dedicated to recording with this process. There are plenty of threads debating the merits and features of the decks but many of us are interested in focusing on how these decks record in 32bit float and what the results are, so I thought this might be useful.

I used my MixPre6 II on Saturday to record Gov't Mule. I ran hotter than I ever had, and I did lower the levels about 2db after the first song which was in the red the entire time. My goal was to run hot, but not super in the red at all times hot. I ran 4 channels, Schoeps MK41's Hypercardioid, and Superlux S502 Cardioid. Here are my thoughts:

I started recording in 1971. It was really hard, really hard to watch levels run regularly in the red after 48 years of avoiding the red. I did it, but I figured how hot to run will be a gradual process.

The results though were excellent! There was nothing even close to distortion. I opened in Soundforge which is what I like to use nest. I transferred the poly file to a stereo file for the Schoeps and a stereo file for the Superlux. On both files I lowered the gain on the first song 2 db and then the entire file another 2 db. The files looked perfect and sounded great. I see obvious advantages , especially when the levels at the start of the show are much hotter than expected.

The learning curve might just be does anything matter? Is any gain too much? Do I care that I have to lower the gain in post if it sound great? Will it at any point with high hot gain sound compressed? These seem to be the details that we will all be looking at, and there probably will be a few differing opinions just like in all of our recording techniques. However there is much more freedom. After 48 years I do not make too many mistakes and I know my mics and most local rooms, but...this was really cool, I totally look forward to using the deck more. Tonight I will record 6 channels at a DSO show with different mics and while I do not plan to run superhot,  will push my levels into the red with confidence.

[spyder9]

Do you have any screen shots of the 'before & after' during Post Edit?

[jerryfreak]

Will it at any point with high hot gain sound compressed?

in absence of using limiters it shouldnt

[Gordon]

Do you have any screen shots of the 'before & after' during Post Edit?

check this out!  this is from

https://www.sounddevices.com/noise-in-32-bit-float/?fbclid=IwAR1gJr5l4Bfo1GMNZXvLMqa_hWC2k1Sf9vk2tZoD7tdcz1K0GTsWcgYpRUY

I opened the one that says "all 3" in iZotope and saved the clipped one by itself.  As you can see it's +31db and is full of distortion etc.  Lowered the gain to just below clipping and it looks and more importantly sounds perfect!  I'm sold.....

[Paul Isaacs]

The only things you need to worry about with the MixPre-II in 32-bit mode are:
1) The microphone itself clipping!
2) Not exceeding the +12dBv (+14dBu or 11 volts p-p) maximum input on the MixPre's mic input. Good luck with that!

[EmRR]

2) Not exceeding the +12dBv (+14dBu or 11 volts p-p) maximum input on the MixPre's mic input. Good luck with that!

^ This.

A lot of hot modern condensers will clip that, then 32 bit float does nothing for you. 

[jerryfreak]

i suppose for every recorder there is an optimum gain level that will offer maximum S/N

at some point adding extra gain just to remove it later can only add noise unnecessarily, right?

[Gordon]

2) Not exceeding the +12dBv (+14dBu or 11 volts p-p) maximum input on the MixPre's mic input. Good luck with that!

^ This.

A lot of hot modern condensers will clip that, then 32 bit float does nothing for you.

explain like I'm an idiot please

[jerryfreak]

2) Not exceeding the +12dBv (+14dBu or 11 volts p-p) maximum input on the MixPre's mic input. Good luck with that!

^ This.

A lot of hot modern condensers will clip that, then 32 bit float does nothing for you.

DPA MMP-A says maximum output voltage is >5V rms/ >16V peak but youd prob have to be recording jet engines to get it to output that hot

[EmRR]

2) Not exceeding the +12dBv (+14dBu or 11 volts p-p) maximum input on the MixPre's mic input. Good luck with that!

^ This.

A lot of hot modern condensers will clip that, then 32 bit float does nothing for you.

explain like I'm an idiot please

If it's clipped....it's clipped.....you can turn it down.....but it's still clipped.....

A TLM103 will exceed that input level anywhere close to a drum kit.  As will any Sennheiser MKH mic.  A loud show with a lot of subs blowing out the bass will make a lot of mics output that kind of voltage if you are near the stacks.   You might still need a pad on the mic or the preamp. Wind noise or vibration will definitely make levels like that, and if it clips it's harder to clean in post.  You still have to set levels with an eye on not turning up too much, there's still a ceiling, it's just (confusingly) higher than it was, and past a monitor-able level. 

The benefit to me seems to be more from the other end, not having to turn things up a lot in quiet ambient scenarios, especially when you might have unexpected hot transients (thunderstorms?), you can leave it low knowing you have a ton of headroom, without paying a digital penalty for that low level.  Recording loud sources that are very even in volume like most people here do, there's not as much to be gained.  The guy next to you who starts yelling and exceeds 0dBFS can be turned down if your were recording at -6 or -12 dBFS and he pegs the meter, he might not be distorted.  He's a different sort of problem....

[Gordon]

I guess I just don't understand the specs listed to watch out for.  I looked up the tech specs of my Gefell's and don't see the same things.  I've never been good at the tech aspect of all this!

[EmRR]

I guess I just don't understand the specs listed to watch out for.  I looked up the tech specs of my Gefell's and don't see the same things.  I've never been good at the tech aspect of all this!

I wouldn't even bother looking at theoretical possibilities with mic specs, just know this 32 bit thing is not a free pass to ignore gain, it can't save everything.  Most mics give you a max SPL for a 1% distortion, but that doesn't tell you what level they will output in a clear manner. 

[aaronji]

From what I have been able to gather, none of these machines actually use 32-bit floating point converters. They use several 24-bit integer converters at different gain levels and then the data is combined and converted to 32-bit float. So I guess it will depend on the implementation to some extent. Sound Devices patented their method, I think, so it will likely be different in other brand's recorders.

I guess I just don't understand the specs listed to watch out for.  I looked up the tech specs of my Gefell's and don't see the same things.  I've never been good at the tech aspect of all this!

Mostly mic sensitivity and SPL. See the table at Sengpiel. It won't be easy to do with most mics, but still possible!

The guy next to you who starts yelling and exceeds 0dBFS can be turned down if your were recording at -6 or -12 dBFS and he pegs the meter, he might not be distorted.  He's a different sort of problem....

That's what analog limiters are for! You'll have to do something to him in post regardless, right?

[EmRR]

The guy next to you who starts yelling and exceeds 0dBFS can be turned down if your were recording at -6 or -12 dBFS and he pegs the meter, he might not be distorted.  He's a different sort of problem....

That's what analog limiters are for! You'll have to do something to him in post regardless, right?

Yeah, or RX7 type cleanup.  If it's splattered with a bunch of distortion harmonics, it's a lot harder to clean. 

[aaronji]

Here are a couple of interesting posts from DSatz on this topic from the F6 thread: http://taperssection.com/index.php?topic=190161.msg2304803#msg2304803 and http://taperssection.com/index.php?topic=190161.msg2309381#msg2309381.