32 bit float - deamplifying peaks results in flattened peaks

[Tim Lookingbill]

Had to make a correction. It was the mac app "Coaster" version 1.1.3. I made the corrections in my previous posts.

[steve]

So are you suggesting that the peaks above 0dB are being flattened by the sound card before they arrive at Audacity?

Yes, though with some hardware setups clipping could occur before the signal even gets to the sound card. For example, if you were recording something via a mixing console and massively overloaded the mixer input, then the mixer channel preamp would clip the signal.

If so, under what circumstances is anyone able to take advantage of Audacity's 32 bit float's ability to store beyond-peak information?

While your working with the audio (editing and processing).
Tim Lookingbill gave a good example - when using an effect (such as the Equalization effect), the signal could (depending on settings) be boosted higher than 0 dB. If the audio data is an integer format (16 or 24 bit) then the audio would be permanently damaged. Integer formats cannot go above 0 dB, but if it's 32-bit float, then the waveform above 0 dB is still there undamaged, so you can simply attenuate (amplify it by a negative amount) to bring it back into the "valid" range below 0 dB.

[kozikowski]

Without that 32-bit thing, applying effects and production would be a nightmare.

OK, We're going to equalize to boost the crispness of a reading. First step, reduce the volume of the work to where you think it needs to be so it doesn't clip after you apply the filter.

What?

Watch me and get off the bus one stop before I do.

I started using a new process for AudioBook reading and mastering. The first step is a tool that changes the volume of the reading to meet audiobook standards. Then run Limiter to bang the tips of the blue waves down so Peak standard is met (overload, basically). It's not unusual for the peaks to go over 0 after the volume step. Soft Limiter is a tool that rescues the normally illegal peaks and gently pushes them into compliance.

If your noise is OK, you're done and nobody can tell we did anything to it.

32 floating is just the handiest thing.

However, no good deed ever goes unpunished, so you have to pay the piper when you export your work. 44100, 16-bit, Stereo (the outside world) is less accurate than Audacity internal, so a dither signal is added to the work to keep the downconverting errors from lining up and becoming audible.

And Do Not try to export the work while some of the sound is above 0. The destination sound formats will whack them off permanently.

Koz

[willbfree]

Thanks everyone this was extremely informative!!!

[Tim Lookingbill]

Sometimes the conversation is relatively sedate - everyone remains calm - and the levels can be set at 100% without any peaks shooting out above. But sometimes the interviewee gets worked up and starts shouting or whatever, so I have to transfer that entire conversation at, say, 75%. And doing it at 75% makes me concerned about the quiet parts - I've worried that at some point in the future, some future editor will want to amplify the quiet voice and they will be very upset that the digitization was only at 75% instead of 100%.

You might find if it does exist some type of software that maintains constant volume levels like cable TV set top boxes provide when watching movies that have scenes of loud explosions followed by quieter scenes of actors talking. Maybe Steve and Koz know of a plugin. Maybe check your system prefs for some type of "maintain volume level consistency".

Before boosting those calm quiet parts recorded to cassette with a mic feed, you might check if this raises the noise floor especially tape hiss by first listening and raising the volume on your system. This is the amazing thing about digital editing (amplify or limiter effect) vs analog gain (through capture software i.e. Audacity/Coaster) in that digital does a remarkable job of replicating the sound nuances when increasing analog volume. I do this volume increase test using the OS volume slider vs amplify or limiter listening on headphones a lot in Audacity on my MacMini. Sometimes depending how good my EQ curve sculpts the sound digital volume increase sounds a whole lot better than raising the OS system volume slider on the unedited version.

When I used Coaster to record music off the cable TV line out I could raise and lower the gain to bring up the quiet parts live as I listened on headphones on the Powerbook. I really watched clipping indicators intensely. That Moorcheba example I posted previously has noticeable volume increases I can hear on the CD-r in my car. It wasn't really that much. If you can listen to your cassette live as it is being recorded in Audacity checking gain/clipping levels it may or may not be difficult adjusting gain in the quiet parts. I remember with Coaster it was quite sensitive to being clipped making live adjustments this way. Had to keep my finger on that slider watching for red clip indicators. It was tedious though.

Try recording in Garageband using high quality 24bit setting in preferences/turn off Normalize and all effects in both Instruments & Master Track and do a live volume increase. Don't know if you can do this live in Audacity.