Signal Generator plugin outputs 24 bit level waveforms in 32 bit float container

[XJENSEN]

Problem with the Signal Generator plugin (both as insert and as AudioSuite). It doesn't seem to generate proper 32bit float waveforms, but rather clips them at 24 bit level, even in a 32 bit float session!

Steps to reproduce: (example for insert mode)
1. Create 32 bit float session.
2. Create Aux
3. Insert Signal Generator (e.g. 440Hz, 0dB, *RMS*)
4. This will obviously clip the Aux output as the peak will be above 0dB for a 0dB RMS sine. So turn down the Aux level (fader).
5. Observe that the sine keeps sounding clipped, i.e. the 32 bit headroom is not used to restore the sine!

Same behaviour is observed with AudioSuite: Although the plugin generates a 32bit file, it's actual contents are clipped to 24 bit level and are non restorable.

It thus seems that the plugin is not outputting proper 32 bit waveforms, but rather 24 bit level in a 32 float container.

[Top Jimmy]

Creating a 32-bit float session is simply setting the default session audio file format to 32-bit float. This has nothing to do with the DSP and bit depth of the processing used in the signal chain. Honestly, it's not surprising that the signal generator code is still only 24-bit fixed point. There's no performance reason for updating it that would make investing the man-hours to change it worthwhile. If you do want to drive the signal above 0 without permaclipping, just follow the generator with a trim plugin and use that to increase the gain.

[XJENSEN]

Thanks. That's actually a very helpful answer!

I understand that the Signal Generator stems from an era where 32 bit was not a thing. And I understand that Avid has more pressing issues to resolve. With you there.

I use the Signal Generator to perform various tests regarding gain staging , etc. So it would have been useful if it actually were 32 bit capable. But the workaround with the Trim plugin after the Signal Generator does sound usable!

[arche3]

Originally Posted by XJENSEN

Thanks. That's actually a very helpful answer!


I use the Signal Generator to perform various tests regarding gain staging , etc. So it would have been useful if it actually were 32 bit capable. But the workaround with the Trim plugin after the Signal Generator does sound usable!

what type of testing do you do?

[XJENSEN]

Originally Posted by arche3

what type of testing do you do?

I was verifying the performance of some down-the-line plugins w.r.t. gain staging behaviour / distortion. Makes sense to use the Signal Generator for this. But it's apparently not compatible.

I reported this to Avid in Case 03842300 on 12/10/2019.
So... It has taken them 4 months to review the case, with today's feedback that 'engineering was not able to reproduce the case'.

They requested me to reproduce it on my end and make a movie, which is what I did.

Now let's see what they make of it. What good is it to offer a 32 bit float session format when their stock plugins aren't even compatible with it.

[JFreak]

Many other plugins operate in 24bit internally as well, it is not just signal genny. Many plugin vendors even advertise it as a feature that their plugin distorts as a caution when 24bits are used so that you would do better gain staging.

Also you have no idea whether plugin resamples to 96kHz so even in a gazillion terahertz session some plugins would operate at 96kHz whether you liked it or not.

[XJENSEN]

Well, I believe you may be right about these plugins. And since I started using more and more outboard gear, keeping track of proper gain staging has become a must anyhow, in order to be able to mix outboard inserts with plugins. It's just that I had expected the Signal Generator to be usable as a 'test tool' in some scenarios. But the workaround of putting a Trim plugin after the Signal Generator does the job.