How to Bass Boost a song?

[Tim Lookingbill]

Thanks for the clarification, Steve.

This subject got me to do some more research to confirm what I thought was an industry established standard (in order to prevent damage to audio equipment) of a max peak level of -12db for commercial CD releases which I found your wiki link Redbook standard didn't make clear. It appears from this article...

http://www.chicagomasteringservice.com/loudness.html

...you can go as high as -0.2 dbFS just under clipping. But as you've indicated this isn't what damages audio equipment but the clipping that introduces added harmonics that changes the timbre of the initial sound shape (such as in the form of harsh rumbling in low bass signals that wasn't there before) that does the damage. So I surmise to keep it safe we should be listening for changes in the character/timbre of the original sound referred to as harmonic distortion caused by clipping during editing.

But this doesn't explain why the severely clipped first sample I posted doesn't cause damage or audible distortion on my car's audio system? Mind you, because it's already so loud, I only play this at half volume on my car's 1997 Pioneer CD head unit (from Walmart), through a 250watt Alpine amp (35 watts RMS to each speaker) which is loud enough to be heard over road roar driving 60mph down the highway with the windows down which according to Crutchfield is around 80db. However, any frequencies around 40Hz can't be heard.

Maybe it isn't about clipped digital signals at all but about distorting the sound initially with edits, clipped or not, that might cause excessively unbalanced speaker excursion. This would explain why high pitched thonky, thin sounding kick bass sounds from '70's & '80's recordings with a -17dbFS RMS limit (according to the article) can't be amplified on my system without distortion as loudly as today's big, fat bass signals even when their digital waveform is clipped.

[Robert J. H.]

Thanks for the clarification, Steve.

This subject got me to do some more research to confirm what I thought was an industry established standard (in order to prevent damage to audio equipment) of a max peak level of -12db for commercial CD releases which I found your wiki link Redbook standard didn't make clear. It appears from this article...

http://www.chicagomasteringservice.com/loudness.html

...you can go as high as -0.2 dbFS just under clipping. But as you've indicated this isn't what damages audio equipment but the clipping that introduces added harmonics that changes the timbre of the initial sound shape (such as in the form of harsh rumbling in low bass signals that wasn't there before) that does the damage. So I surmise to keep it safe we should be listening for changes in the character/timbre of the original sound referred to as harmonic distortion caused by clipping during editing.
...

The article says no such things.
Let's take the extreme example of a clipped signal: A square wave (-1 -1 -1 1 1 1 -1 -1 -1..., at full scale)
The big problem is the fast change from -100 % to 100 % which can cause the speake's membrane to "overshoot"--always depending on the actual reaction times of the whole system.
The -0.1 to -0.3 dB security head room for inter-sample overs is not even nearly enough (e.g. see the "True Peak" level measurement in the ebu128 recommendation).
You can test it approximately as follows:
- Generate a square wave tone (just use the default settings for the other parameters)
- read the dB (amplify effect), should be (-)1.9 or so.
- call the nyquist prompt and enter

Code: Select all

(resample s *sound-srate*)

- read the dB peak again.
- do the same with a square wave that has no aliasing.

The difference is remarkable.
You can of course test other audio with this trick, however, it isn't an official method, it only shows what could happen to the output.
I'm fairly convinced that the intersample difference has the greatest impact, apart from e.g. DC offset.

[Tim Lookingbill]

That's an interesting test, Robert, even though it's over my head and skill level. IMO music isn't made and checked for corruption by distortion based on testing one square wave pattern. No one listens or cares what happens to square wave patterns pushed beyond their digitally allotted headroom.

Other than that how do you explain the lack of distortion in the heavily clipped sample I posted? Not here to debate what an article says. This thread is about how to boost bass and make it loud digitally and pinpoint causality to any artifacts as a result to distinguish whether it's sourced from the file or through system output or a combination of both.

The article just confirms there are commercially released CD's whose mastering pushed the headroom to -0.2db with no noticeable distortion. I listened to the samples in that article and couldn't hear any improvement or distortion, they're just a bit louder and brighter. What's misleading about that article as is in all of these types of Loudness War discussions is they attempt to prove their premise on songs that are already loud, noisy and peppered with "artful" distortion making it impossible to hear any artifacts caused by brick walling. It's pointless to make arguments on something no one can hear.

Did those songs need to be brick walled? No. They were loud and noisy to begin with. Does brick walling produce distortion? Well if I can't here distortion in an intentionally clipped (beyond brick walling) entire waveform on headphones as I posted above and no one can explain why, then I don't see the point to the question.

I'll give you an example why testing a square wave isn't going to hold water musically speaking. I discovered something interesting editing one bass signal wave when applying the Low Pass bass boost method on a duped stereo channel converted to mono. After normalizing the mono bass signal to 0db using Amplify I got a clipped waveform. I zoomed in and selected this wave and used Amplify to remove the clip. The waveform retained its original rounded top (no flat top). I muted the stereo channel and played only the mono bass channel and I got a slight but very audible crackly noise on the repaired waveform. When I applied the same Amplify fix to the same bass wave in the stereo channel there was no crackly sound.

Can anyone explain why?