Topic: Roland R-07 32-bit floating point!

[adrianb]

No downside in keeping the safety track active is there?  I would think just for peace of mind, if anything.

The theory being that the R07 uses the second track for the “hybrid limiter” which is much better than the regular limiter. On the evidence of my gig last night I would be happy to rely on the improved limiter, rather than safety track, for most shows because it’s easier and the safety track does introduce some noise.

That said if it was a show I was desperate to get right I would probably revert to the safety track, or use the 32-bit float Tascam I am buying when it becomes available in the UK.

The R07 is just such a neat little device I can imagine I will want the Tascam in my packet too often.

[TheJez]

Just a quick update regarding the initial intension of this topic and the developments so far:
My initial thought was to use a weighted average of the samples of the main track and the safety track, where a louder sample would get a higher percentage of the safety track sample and a softer sample would get a higher percentage of the main track sample.
I had quickly abandoned this idea, as it would mean that each output sample would get 'poluted' with data from the noisier safety track, even when not necessary at all.
Being inspired by the SD patent I couldn't put this fully to rest and continued to work on a 'safety track merger'. My method is a bit different than the method described in the patent but addresses the same issues. I've made quite some progress so far. The program currently works in two steps: The 'Preparation Phase' and the 'Merge Phase'.
In the 'preparation phase'
- The program reads the main and safety tracks, converts them to 32bit floating point, throws away all info below 10Hz to get rid of any DC component (including the 'varying DC' also addressed in the SD patent).
- It counts the number of clipping samples in the main track (for left and right channel). If there are no clipping samples, there is no need to merge. A list of clipping samples (sample number and timestamp) can be exported to the clipboard for evaluation purposes)
In the 'merge phase':
- A 'window' (of currently 64 samples) slides sample-by-sample over the main and safety track.
- For each window, the gain factor between main and safety track is determined as accurately as possible and the safety track is amplified by this gain factor to make it match the main track window.
- A 'difference' between main and amplified safety window is calculated. For a non-clipping window, this difference will be small. For a window including clipping (or other artifacts e.g. caused by analog stage overloading), the difference will be bigger.
- When main and safety windows are 'similar enough', the main window is added to the output. If they are 'too different' (i.e. there is clipping or other artifacts),  the safety window is added to the output.
- Because of the 'sliding window' principle, a slow (64 sample) cross-fade between main and safety track is applied when switching between the two. So there is no hard transition from sample-to-sample. This should mitigate transition effects caused by (hopefully very low remaining ) inaccuracies of the gain factor calculation.

All is working, except for the part where the main or safety window are added to the output. Still working on that...
Thanks for your interest  I'll keep you posted...

[Gutbucket]

Clever.  Like that you've set it up in a relatively simple, well managed way.  Curious about the repercussions of detection window length "tuning".

Cool that you've continued work on this and thanks for the update!

[TheJez]

Yes! Merging is working! I completely did not optimize the program for speed, but the numbers are not too bad:
- Preparation is very fast, ~10s for 30 minutes of audio
- Merging is a bit slower, roughly 4x 'realtime'. So ~7.5 minutes for 30 minutes of audio.
Both are substantial slower when 'visualize' is enabled. These only add nice dancing lines to the user interface, so are not needed.
Now I just need to clean up the code a bit (lots of leftovers from debugging/testing).
Below the screenshot of the user interface at the moment and a 32bit floating point merged R-07 recording from the files so kindly provided by Adrian. Notice the samples going above 0db! These were the parts were the main track was clipping. I did not add a normalization function, as your DAW can do that very well. It now also clearly identifies at which parts the safety track was used (samples > 0db), so I thought it would be better to keep it this way. The program also creates a log file of the merging, to show for what parts the safety track was used, e.g.:

...
00:00:25.196870: Right channel started fading in safety channel
00:00:25.197777: Left channel started fading in safety channel
00:00:25.197800: Left channel started fading out safety channel
00:00:25.198276: Right channel started fading out safety channel
00:00:25.608480: Left channel started fading in safety channel
00:00:25.609387: Right channel started fading in safety channel
00:00:25.610022: Left channel started fading out safety channel
00:00:25.610952: Right channel started fading out safety channel
00:00:25.896054: Right channel started fading in safety channel
...

[grawk]

That is awesome! I wonder if it would work with the lectrosonic spdr safety track too

[TheJez]

That is awesome! I wonder if it would work with the lectrosonic spdr safety track too

There is no reason why it shouldn't work for another device. Currently, the only conditions are:
- Input files shall be stereo 16 or 24 bit wav files
- They shall be equal in length (up to the sample) and perfectly in sync
- They shall have identical sample rate

As you are asking about this particular recorder, I assume you have one of those. It would be awesome if you would be able to record 'anything' with it (e.g. your stereo playing some music for a few minutes) with the record level just a bit too high to make the main track clip. If you could provide the files I could do some testing. Or if I would provide the program, you could do the testing. However, if for some reason some tweaking of the program is needed, I guess it would be more convenient if I would get the files... 

[grawk]

Yeah, I have one. I will record something this afternoon.

[TheJez]

Yeah, I have one. I will record something this afternoon.

Great! No hurries…

[adrianb]

I actually recorded another gig last week where the main track clipped if you are interested.

[TheJez]

I actually recorded another gig last week where the main track clipped if you are interested.

Yeah, that would be great! The more the better…
Are you interested in getting the merged file of your previous recording?

[grawk]

https://drive.proton.me/urls/AYQMC4TW4W#BdVrBJKwCWxu

4015gs -> SPDR 48/24 with safety (all 4 channels in 1 file)

I tend to run very conservatively so I haven't needed the safety track. 

[adrianb]

Yeah, that would be great! The more the better…
Are you interested in getting the merged file of your previous recording?

Is the merged track actually an improvement over the safety track?

If you can send the link to your file sharing I’ll send a couple of files.

[grawk]

So I'd think it'd work the same way it's supposed to work on dual adc converters. You get the advantage of being able to run loud to maximize SNR, while protecting yourself from overage.  The only time you have the increased noise floor is at loud points where the noise will be far below the actual signal level.

[TheJez]

Is the merged track actually an improvement over the safety track?

If you can send the link to your file sharing I’ll send a couple of files.

To be honest: For this particular recording, there is no audible improvement over the safety file. Even the quietest parts (crowd noise between the songs) are well above the recorder self noise, even on the safety track.
I guess most benefit can be reached for recordings with very high dynamics, so very quiet and very loud parts.

Maybe you could turn the files to flac and zip them, then upload to wetransfer.com and pm or mail the link to me. They allow sharing files up to 2GB in size. I think you may still have my email address from the last time…

[TheJez]

So I'd think it'd work the same way it's supposed to work on dual adc converters. You get the advantage of being able to run loud to maximize SNR, while protecting yourself from overage.  The only time you have the increased noise floor is at loud points where the noise will be far below the actual signal level.

Yes, exactly. So we’ve turned this device into a 32bit floating point multi-adc recorder, with the only difference compared to others that the combining is done in post instead of in realtime… And you need to set the record level to a sensible value, although now we have 20dB more headroom to play with.