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Roland R-07 32-bit floating point!

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TheJez:
Summary: Could the Roland R-07 be a multi-ADC 32-bit fp recorder in disguise?

Sorry guys, I must admit: The title of this message is a bit of a click bait. At first I wanted to put a question mark at the end, but then I thought: “Anybody seeing that will think it’s a post from someone too lazy to read the spec sheet of the R-07 and won’t even bother to further read this post.” I am hoping to get interest from people knowing/owning the Roland R-07 and people interested in 32-bit fp recording…

Some background: Since a little while I am looking for a replacement of my Edirol R-09HR. When going through all this information on TS I concluded that 32bit-fp multi-adc is the way to go for my needs. So when someone on TS very kindly offered me a Roland R-07 for a very reasonable price, I still turned him down “because I want to go 32bit”… However, this offer made me think…

A couple of years ago I read about the R-07 and about its safety track, recorded at a lower volume, as a backup without distortion if the record level was set too high. That sounded like a very useful feature! On November 29, 2019, someone wrote on TS about this device: “I think the dual recording levels is far more useful than remote app for stealth conditions. I now go in with the levels pre-set and never look at the device, or the app, or worry about levels at all.” And also: “With the dual recording I just set it to 48 and then forget” Hmmm, sounds familiar? I’ve often seen very similar remarks while reading up on 32-bit multi-adc recording. Set-and-forget, how great would that be!

And now I started wondering about the signal path of this safety track on the R-07. So I went through all 39 pages on TS about the R-07 to see if there’s any info about it. All I found was someone claiming on December 19, 2018: “Metering and dual recording happen post-ADC.”. Would it really be true that dual recording is completely post-ADC? Personally, I find that hard to believe when looking at the possible sources of clipping distortion due to too high record level in this recorder. I guess there are two potential places where clipping could occur:
1)   At the analog input stage ((amplified) input signal too hot to handle by the analog components)
2)   In the ADC (signal coming into the ADC too hot, resulting in clipping samples)
(I can’t think of a probable, realistic cause of clipping post-adc in this device)

Now if the signal is clipping, either due to 1) or 2), then reducing the level post-ADC by e.g. -20dB and then storing that as a safety track will not solve the clipping! So it means there must be two ADC’s: One for the normal track, one for the safety track. And possibly, there will even be two analog stages! This would result in the following signal paths:

(see attached picture)

There would be two identical paths, with only a difference in the applied gain in the input stage. For the normal track, the gain 'x' as set by the user is applied. As we know, in 2xWAV mode, this is a value between 42-100. For the safety track, a gain of ‘x-42’ is applied. (If I’m correct, in the latest firmware, the offset of the safety track can be selected from -6/-12/-20db. I guess ‘-42’ would then match a -20db reduction…)
Now if these assumptions about the signal path would be correct, then we have a device very similar to the current 32-bit devices. The only thing missing is a piece of logic/signal processing that’s taking the samples coming out of the two 24-bit ADC’s and combining this into a 32-bit float sample. I know this part is the real ‘heart’ of 32-bit float multi-adc recorder, but… is this something that really has to be done in real-time within the device?? I’d say no, not necessarily… As long as you store the output of the two ADC’s, you could combine these into 32-bit float anytime you want!

This missing piece of logic could very well be implemented as a software program running on a PC. The required algorithm doesn’t seem extremely complex, imho…
So what do you think? Could this potentially work? Where did I go wrong in my thinking process? Hope to hear your thoughts…

aaronji:
The 32-bit floating point recorders split the incoming signal into two (or more) gain-ranged streams which have different gains applied before conversion.

TheJez:

--- Quote from: aaronji on September 23, 2024, 09:36:07 AM ---The 32-bit floating point recorders split the incoming signal into two (or more) gain-ranged streams which have different gains applied before conversion.

--- End quote ---

Exactly! But isn’t the R-07 doing the exact same thing, but then to get the normal file and the safety file?

aaronji:
No. The R07 doesn't split the signal into two parts. It sends the whole signal down both paths.

TheJez:

--- Quote from: aaronji on September 23, 2024, 10:19:55 AM ---No. The R07 doesn't split the signal into two parts. It sends the whole signal down both paths.

--- End quote ---

Then I think that, even after reading all the threads about 32 bit multi-adc recording, I still seem to miss some details about the technology behind it. Wouldn’t splitting the signal as you describe introduce all kinds of frequency components that are not part of the original signal? Isn’t the full signal fed into two adc’s (although at different levels) and isn’t then the output of the adc’s combined by taking e.g. a weighted average of the two samples, where the applied weight depends on the actual signal strength?
Hopefully you can elaborate a bit on the splitting mechanism you mentioned to help me understand…

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