bass reconstruction processors

I'm very curious about these devices. Any experts to comment on them. Are they versatile? Can they offer subtle/tasteful bass reconstruction as well as drastic differences? Anything they truly sound bad with?

Don't use them. Ever.
No.
VERY rarely, and when they do, it's not great in any case.
Everything.

They're effectively nothing more than a crossover with one band, quasi-parametric EQ, with line-driver built-in. They offer GREAT options when looking to mildly overdrive your amplifier's inputs, all they way to straight-up clipping the CRAP out of 'em. Distortion additions that I know *I* have never ever liked the sound of. I've never used them, I've never recommended them, either. If you ask around here about them, chances are you'll get very similar responses from all of the more knowledgeable members.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Ditto.

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i third that

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I'm noticing a common trend here. ;) Lol

As far as what they actually are, I've read they use an algorithm to register detectable harmonic overtones and fill in lower fundamental notes. This is in reply to haemphyst, is it possible that the units that seemed to be more of the line-driver, quasi-parametric eq deal were inferior? Just wondering, not trying to insinuate anything.

The reason I was curious about the units at all to begin with is because I have quite a few recordings, like classic rock and other older music, that is missing a lot of the fundamental bass notes almost entirely. Also, even some modern recordings where the fundamental bass is inconsistent (missing more in some bass notes than others). I'm familiar with how an actual bass guitar sounds, so I know you can get "deeper" sounding notes several frets up versus open strings in some cases, but the issue seems rather drastic in some recordings.

Then again, there is another part of me that likes to preserve the integrity of the original audio, even if it is flawed. I guess my ideal scenario would be to compensate about halfway (hence why I asked if bass reconstruction could be used in a subtle context). However, I also see another issue. Sometimes the fundamentals should be less present due to timbre of a particular instrument or how it's used. I'm afraid using bass reconstruction could result in very poor, one dimensional depth in regards to musical texture.

Sorry for the long-winded post. I think you guys would to relieved to know I'm leaning toward not using them though. ;) Any other thoughts or comments? I'm all ears.

gandalf91 wrote:

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... they use an algorithm to register detectable harmonic overtones and fill in lower fundamental notes.

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How do they know the tones are NOT the fundamental? (IE - they assume. They'd probably give you 30Hz from a 60Hz supply.)
(Reminds my of guitarists that use octave droppers to act as bass guitars - though that is planned & intentional.)

That's quite different to boosting existing bass.

oldspark wrote:

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gandalf91 wrote:

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... they use an algorithm to register detectable harmonic overtones and fill in lower fundamental notes.

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How do they know the tones are NOT the fundamental? (IE - they assume. They'd probably give you 30Hz from a 60Hz supply.)
(Reminds my of guitarists that use octave droppers to act as bass guitars - though that is planned & intentional.)

That's quite different to boosting existing bass.

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By ratios resulting from the overtone series...it's really not all that fantastic as it seems. It's not assumption.

https://en.wikipedia.org/wiki/Harmonic_series_%28music%29

gandalf91 wrote:

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The reason I was curious about the units at all to begin with is because I have quite a few recordings, like classic rock and other older music, that is missing a lot of the fundamental bass notes almost entirely. Also, even some modern recordings where the fundamental bass is inconsistent (missing more in some bass notes than others). I'm familiar with how an actual bass guitar sounds, so I know you can get "deeper" sounding notes several frets up versus open strings in some cases, but the issue seems rather drastic in some recordings..

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if you are noticing loss of bass in recordings then you most likely suffer from recordings or cd rips with a low bit rate. this it typical when you download audio or when you rip a cd without paying attention to the settings or your program you use to rip cds. for instance, if you rip a store bought cd into iTunes without changing any stock settings then the audio will get compressed to 192kbps. that is way too low to ever sound good on a half decent car audio system although you wont notice the difference with ear buds.

this is a downfall with medium to high end systems is that they will audibly bring out the flaws in a poor audio rip. the bass will sound lower than normal and undetailed and the highs will sound like there is a constant "shimmer" (this is the best i can describe it) in the background.

go on your computer and find the songs that you say sound bad in your car and pull up the properties of the song, it will tell you the bit rate and if its lower than 320kbps then this is more than likely your problem. even if it says it is 320 it could still be the problem because it could be a song that was previously ripped in a low bitrate and then ripped again in 320. its exactly like making copies on a copy machine. if you copy a picture with a low quality copier first and then take that copy and copy it again with a high end copier it will still only look as good as what you got from the first low end copy machine.

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I always go 256kbps or 320kbps. I know the shimmer you describe though. I've noticed it very blatantly in anything less than 128kbps *shutters*. I've actually heard some 160kbps songs with decent bass...I'm pretty sure lack of bass in some cases is just the old recording itself. As for inconsistent fundamentals, if worst comes to worst, I could just run some parametric EQ touch up on the particular songs in question. Most songs in my collection sound pretty excellent on my system though. ^_^

well, like i said, just because it says 320 doesnt mean it actually is. its only going to display the bit rate that it was last compressed to. i have some songs that are supposedly 320 and they sound horrible, with no detail and it sounds like im listening to the song through a pillow or something but other songs in the same cd or file sound great. this is the only explanation i can come up with that fits the symptoms.

and once again, anything that was recorded in the pre cd era and was not ripped off of a remastered disc or possibly was converted directly from a vinyl record, 8 track, etc, straight to some random dudes computer and then was seeded for download might say 320 on the label but it will never sound like a professionally remastered disc.

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Yeah, I know what you mean.

gandalf91 wrote:

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By ratios resulting from the overtone series...it's really not all that fantastic as it seems. It's not assumption.

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That assumes a non-integer harmonic - eg, if 60Hz & 90Hz are present, it could be assumed that 30Hz is the fundumental - but that is an assumption...

It's a lot of Fourier series matching to determine "matched" harmonics - ie, that 60Hz & 90Hz are from the same source.

I'd presume DSPs are used...

oldspark wrote:

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gandalf91 wrote:

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By ratios resulting from the overtone series...it's really not all that fantastic as it seems. It's not assumption.

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That assumes a non-integer harmonic - eg, if 60Hz & 90Hz are present, it could be assumed that 30Hz is the fundumental - but that is an assumption...

It's a lot of Fourier series matching to determine "matched" harmonics - ie, that 60Hz & 90Hz are from the same source.

I'd presume DSPs are used...

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The ratio between any two given harmonics are always the same, regardless of the instrument. For example the first the ratio of the second harmonic and first harmonic is always 3:2. If 60hz was first harmonic and 90hz the second, then yes, 30hz would be the fundamental. Yes, they could be the sixth and ninth harmonic, resulting in a 10hz fundamental, but sixth and ninth harmonics are likely to be easily discernible from first and second, even by terms of relative amplitude attenuation.

You bring up a good point about the Fourier series and matching or differentiating sources. I hadn't heard of that series before, but I'll read more in depth about it in the near future. All I'm saying is with all the math we've unveiled behind music down to the study of waves, and as you said yourself through the use of DSPs, I'm sure something like this could be accomplished. However, there is always room for error.

I think you are missing my point. And I am being consistent with your Wiki link (which is merely about basic harmonics and does NOT address the methods & algorithms for this device...).


The device samples a low frequency. How does it know there should be a lower harmonic. (Assuming all higher harmonics are integer multiples.)

Hence if you sample your domestic 60Hz (else 50Hz) AC, will it synthesize 30Hz? (Assuming no non-linear loads/interference, all AC mains harmonics will be multiples of the fundumental - namely 60Hz (else 50Hz).)    

Is that clearer?



PS - it has to be DSP but even then there will be assumptions - ie, it is algorithm dependent which IMO must be based on the type of music etc. I can accept recovery (eg, SN ratios <0dB), but the rest is Hollywood stuff (eg, resolving a number plate from a single or few pixels...).

Sorry for my poor explanation, but to me DSPs are so last century....

oldspark wrote:

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I think you are missing my point. And I am being consistent with your Wiki link (which is merely about basic harmonics and does NOT address the methods & algorithms for this device...).

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I know, but idealistic this would be the most basic starting point for developing the algorithms.

oldspark wrote:

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The device samples a low frequency. How does it know there should be a lower harmonic. (Assuming all higher harmonics are integer multiples.)

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Because it would not only sample one harmonic frequency itself! If the fundamental was 30hz (we'll use the same example), it should register a 60hz band, 90hz, 120hz, etc. However, if 60hz was indeed the fundamental, a 90hz harmonic for that source would not exist. The first harmonic would be 120hz. The idea is not to just automatically synthesize an arbitrary note for every sound in the spectrum one octave lower.

oldspark wrote:

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Hence if you sample your domestic 60Hz (else 50Hz) AC, will it synthesize 30Hz? (Assuming no non-linear loads/interference, all AC mains harmonics will be multiples of the fundumental - namely 60Hz (else 50Hz).)    

Is that clearer?

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I'm not exactly sure what you are saying with this last part. Are you referring to the frequency of alternating current noise interference entering the device? If so, would these even bear any harmonics? (I personally do not know), and if it did not, no lower note would be reproduced. The idea being SETS of harmonics are registered, note a single random frequency. Harmonics can again, easily be distinguished between fundamentals by nature of their ratios between other surrounding harmonics. Now if there are multiple sources, I could see SOME room for error like you mentioned.

So the device does not introduce any lower frequencies from what you are saying. IE - it won't assume lower "integer" harmonics.
I got the impression it did....

I'm not sure about lower harmonics. (For example, I don't know that it will fill in a first and second harmonic if a third and fourth is detected.) If the upper harmonics of a particular note are discernibly there though the point (as I've read and understand) is to fill in missing fundamentals (if they are missing). I believe if it detects the harmonics it will scan for the fundamental, and if it returns under a certain amplitude (dB) or is missing all together the device will fill it in. My concern with using them on this issue would be in cases where the fundamental should be sounding softer than the harmonics and whether or not it would pose a problem distorting the harmonic content too much. [For example, the lowest fundamental note on a bass guitar is ~41hz. However, in most recordings, the 82hz harmonic may be heard more loudly than the fundamental. Think about hearing a low electric bass note on a high end system. Now think of hearing a 41hz sine wave. The latter obviously sounds deeper. I would think a possible downside to the processors is that it could mess up the timbre of certain musical sounds.]

I guess I still don't exactly get the last bit of what you're saying. What precisely do you mean "integer" harmonics? I guess I can say, it won't generate "undertones" (harmonics below the fundamental) because those don't naturally exist in music, but I don't know if that means anything along the lines of what you're saying. The math is really there though to make pairs of harmonics very distinguishable from a harmonic and a fundamental. The ratios are all constant no matter what the fundamental note is.

Integer is as per your wiki link - ie, 2nd, 3rd, 4th, .. nth harmonic - ie, "whole number". Not 3/2 etc.

And now we are back to the start.... "....is to fill in missing fundamentals (if they are missing)".
So how does it KNOW if there is a missing fundamental that has been filtered out?
The answer is based on my replies - it requires DSP analysis and then assumptions ie, pre-programed algorithm(s).

If it is inserting assumed fundamentals, then that can lead to amazing effects. (I suspect that is why the others are saying stay away, don't do it etc.)
Detection of existing but quiet frequencies is merely amplification (albeit with noise reduction). And that has the relative amplitude issues that you describe. (Hence the need for recognition and then the pre-programmed algos - ie, that is an acoustic base 82Hz therefore..., or (partly) a grand piano 82Hz, therefore... And that recognition can only be done via full bandwidth assessment.)     


I'm familiar with the type of intelligent programing that is required for that sort of stuff and I reckon I can almost certainly assure you that suitable hard programing does not yet exist. (Face and voice recognition is easier!)

"And that recognition can only be done via full bandwidth assessment"

Ahhh, is this perhaps where our misunderstanding has been all along. To "correctly" use them, as I've read, you're supposed to run them as a preamp (even to any amplifiers you may be running for woofers, mids, tweeters, etc.). They only work by analyzing the full spectrum of sounds (even though they only affect the frequencies in the sub-range). Yes, there are still assumptions such as the amount of amplification to apply to missing fundamentals, but altogether missing fundamentals are not wild guesses/assumptions in this regard.

"I can almost certainly assure you that suitable hard programing does not yet exist."

I believe you. This is basically what I was asking from everyone in my OP. I knew the basics of how they work, just wanted to know how mature the technology was, or if it was still very crude. (The latter seems to be the general consensus). :P

gandalf91 wrote:

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... but altogether missing fundamentals are not wild guesses/assumptions in this regard.

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So yet again, HOW do they guess - I mean, "know"? (You must have read their method??)

Or - do they or do they not insert non-existent harmonics (ie, the first harmonic aka the fundamental). [ You have indicated both.... ]

If you have some link that explains it, cool. But your previous link does not - Wiki knows what the fundamental is.
[ I was thinking of suppressed fundamentals with odd harmonics (flutes, clarinets, etc) versus odd & even (sax) or even only (square, triangular, etc), but that's too hard to tie in with that simple "single fundamental" Wiki example. ]

Or maybe the bottom line, does that device employ a DSP, or is it merely some cute analog filters & mixers?

Okay, this is the last time I'm answering the same, banal question. I mean no personal offense, but you're turning this into something much more complicated than it really is. I've answered this half a dozen times, so here were are again for the last time.

First of all, no the link itself does not make all truths suddenly unveiled...no, one has to take that knowledge of basic harmonics and actually apply it. So let's go with some examples. I pluck an open E on a bass guitar and record it for playback. The low E consists of the fundamental 41.2hz, and varying projections of the overtone series ~82hz, ~124hz, ~165hz etc. Let's say my microphone which I used to record the note was a piece of garbage and only registers frequencies down to 70hz, omitting the 41hz fundamental. Now, using next three harmonics, don't try and say you cannot find the fundamental from those and are "assuming". It is obvious that the common difference between them is ~41hz, yet the lowest note detected is 82. First of all you can simply figure out which harmonic is which by dividing from the difference 165/41 =~4. Hence that is the 4th harmonic in the overtone series. Now in practice, yes, some harmonics from instruments tend not to result from perfect integers, but they are very close. So if I repeated the pattern with 41hz, 81hz, 121hz, 161hz, etc (accounting for some skew [flatness in this case] of upper partials), the world is not suddenly thrown into chaos and the detectable patter shattered! No any sensible person with knowledge of these harmonics can still tell which is which. Maybe in the case of instruments that produce blatant non-integer overtones (like resonant drums and gongs) this might be true, but for the sake of most instruments it is not.

So now on to instruments you propose which suppress the fundamental by nature and produce only odd harmonics (such as a flute or clarinet you say?) I'm honestly not following you at this point. I checked up on some sources regarding flute acoustics and they are capable off producing all integer harmonics. https://www.phys.unsw.edu.au/jw/fluteacoustics.html#harmonics Assuming an instrument does sound such that only odd integers are produced, (low E example again) you get 41.2hz (first/fundamental), 124hz (third), 205hz (fifth), and the 41.2hz is filtered out via the bad recording. Lets divide the two upper harmonics to see how they correspond to one another relatively. 205/124. Our result, 5/3. Immediately it becomes apparent that our integers are 5th and 3rd. What is missing? The fundamental. You can take either 205/5 or 124/3, your pick. Either way you get ~41hz. Not so hard...and certainly not an assumption either. And how should the device know not to fill in 82hz? Because there was no 4th harmonic between the 3rd and 5th, so why should there be one between 1 and 3. It's all a very simple analysis of patterns and ratios. It's nothing more than knowing the math to apply it to very common scenarios.

Now, with the example of even only harmonics, I am not clear on what you mean. Do you mean to say an instrument that produces a fundamental and then evens from thereon in or one that only sounds evens and no fundamental...in which case, for the sake of analysis, wouldn't the second become the new fundamental, the fourth the new second? etc. For the purposes of mathematical analysis it would certainly work. If however, it sounded a fundamental at 41hz, then harmonics at 82hz, 165hz, etc. That would be trickier and probably require relative sampling of things such as the relative amplitude between those two detected harmonics (as higher harmonics diminish in amplitude) and possibly between the rest of the musical content, then some inconsistencies may result.

"Or maybe the bottom line, does that device employ a DSP"

Yes, I believe so. They are a type of harmonic content PROCESSOR. :P

I have not been arguing that these things will reproduce accurate musical content (as I can think of several reasons why they would not), only that there are definitive ways of analysis to find a fundamental pitch. I'm done having this side discussion though. You have repeatedly asked me the same question several times over. I can answer time and time again, but as long as you refuse my proposed explanations I cannot help you. I thank you for your patience and willingness to respond, now let's please just drop it.

Likewise don't take this personally, but I'm sick of asking the same banal question, but you have now indicated it is a DSP (yay!), and that you can't answer what I asked.

Yes, you have provided wonderful basics on harmonics and typical reproduction problems.

Now go and apply that to a collection of sources - a mixture of instruments and styles. (The reason I asked my OQ is because I know what is involved.)

Though not sonically accurate, an Audio Control Epicenter sure does make 70s rock and roll much more enjoyable than without it.

That's the bottom line isn't it?

But 3 others reckoned no, never, etc.
Is that with different music, or audiophiles' on the purity of reproduction?   
Or does it reflect hazards? (I know, the system should prevent speaker, er, ... popping. Besides which I'd assume a simple bypass facility.)


I was thinking how easy this is to do: Start with a self-adjusting parametric equaliser, use its readings for the recognition algorithms, and process accordingly. Web databases could really help (unlike the old days).