why that waveform?

[elan]

hello

i've recorded a ms10 and this is the waveform.. seems pretty strange..

why this happen? is also happened with a microkorg last year

is that a problem?

thanks

[elan]

i mean is all in the upper side

[Kris]

Harmony Central - DC Offset: The Case of the Missing Headroom

[Vogon]

That, I take it is one "note"?
If that's the waveform coming from a single, unmodified oscillator, you have a problem... The drop-out may be in the digital path, but it's not possible to tell from the picture - it's more likely to be the synth if those volume steps are not due to any modulations.
It needs a doctor methinks.

Ah, it's assymetrical?
Some waveforms are assymetrical, though a filter will normally remove a DC offset...
What waveform is it (tri, saw etc.) and is it possible to bypass the filter on that synth?

[mohthom]

If it's a stereo file it means it's more heavily weighted toward the left channel.

[Vogon]

The single circle next to the part name means mono, it's an old mono syth too.

Could be the synth is just adding a DC offset, if it's happening on most patches, likely needs some caps replacing or the like.

[elan]

well those are 4 notes and it's a ms10 with the saw and the filter at 7 and the resonance at 7

i've read this is a problem of headroom.. the logic peak is at -6 but the ms10 volume is at max because i'm going into a preamp with a instrument channel that needs a active d.i. for bass and guitar.. but theoretically should works without d.i. with a keyboard.. so i've put the ms10 volume as loud as i can to avoid the noise floor and i've trimmed the gain in the preamp.

btw now i try to lower the output of the ms10 at half and see if this happen.

[Vogon]

I think that shouldn't make any difference, except for amplitude...

[elan]

ok but the ms10 has done that just that time, usually the waveform is perfect so i don't think are caps.. or anything wrong in the hardware..

[Vogon]

Can you zoom in on the waveform, so we can see a couple o' cycles?

[Vogon]

Oh, and if it's just the nature of that sound/patch, you could try running the synth into a no-resonance, low order, wide-open external filter, as a quick fix - or just live with it - you don't want to be running any audio into an ADC too hot, anyway.

[elan]

ok now i do some try and i repost the waveform zoomed..

could you suggest me a wide open external filter

(what an ADC ? AnalogDigitalConverter? but i'm at less then -6.. isn't hot)


thanks

[Vogon]

Yes, ADC is analogue to digital converter, the image you've posted looks OK, amplitude-wise. There's no headroom problem here - so you don't specifically *need* to "centre" the wavform.

External filters could be anything like a sherman, or even a guitar pedal with a filter. By wide-open, I mean that a low-pass should be set with it's corner frequency at max, to affect the sound as little as possible.

I *think* any device with a buffer or coupling circuits would work though... but I'm not an electrical engineer.

I have a feeling though, when we see the waveform, that it won't be an actual DC offset, the waveform is simply skewed to have a wider excursion in the positive zone, much like a trumpet waveform: I think it's just part of the sound itself.
The clue is that the portions beween the notes seems to be centred around unity...

[elan]

so.. here is the zoomed.. maybe i'm a bit stupid but... if this is a SAW.. isn't normal that goes only on the upper side?

i've tried various thing.. i've tried recording it from the bass amp.. with its active d.i. and i've lowered the volume etcetc.. i got always the same waves.. so isn't a headroom problem.

but if i change the wave.. i use the triangle or the square.. the problem doesn't exist..

so... is normal that the saw is all in the upper side?

[elan]

Originally Posted by Vogon

Yes, ADC is analogue to digital converter, the image you've posted looks OK, amplitude-wise. There's no headroom problem here - so you don't specifically *need* to "centre" the wavform.

External filters could be anything like a sherman, or even a guitar pedal with a filter. By wide-open, I mean that a low-pass should be set with it's corner frequency at max, to affect the sound as little as possible.

I *think* any device with a buffer or coupling circuits would work though... but I'm not an electrical engineer.

I have a feeling though, when we see the waveform, that it won't be an actual DC offset, the waveform is simply skewed to have a wider excursion in the positive zone, much like a trumpet waveform: I think it's just part of the sound itself.
The clue is that the portions beween the notes seems to be centred around unity...

ok great so it's just the saw? the nature of the saw..

[Vogon]

Originally Posted by elan

ok great so it's just the saw? the nature of the saw..

Think so, *looks* like a sawtooth with resonant hi-pass, but I think the ms10 only has lowpass, so it must be the CF and resonance is high...

[elan]

yes is with the cutoff at 7 and the resonance at 7... so all the waveform pass thru and resonates in the highs... the classic ms10 saw

perfect

[jrod9900]

I got nothin'. I'm just a noob. ????

JROCK

[Vogon]

Also like the string waveforms of a string ensemble machine... my fave

[Dan]

It looks pretty normal to me. I don't believe there is a DC offset, as I look more at the total area above, and below zero. They look roughly equal, just differently shaped. There's higher harmonics on the positive side, but it seems more of a synthesis anomaly than something patently wrong.

[PRobb]

I've seen that when recording solo brass. 80% of the waveform is above or below the line. Not DC offset because nothing else recorded with the same setup looks like that.

Not a problem because it sounds fine, but I am curious. Anybody have an explication for why some waveforms are shaped like that?

[Dan]

Originally Posted by PRobb

I've seen that when recording solo brass. 80% of the waveform is above or below the line. Not DC offset because nothing else recorded with the same setup looks like that.

Not a problem because it sounds fine, but I am curious. Anybody have an explication for why some waveforms are shaped like that?

DAMN!

just kidding... I could be wrong, but it has to do the harmonic content. If there are more high frequencies on the + side of the polarity it will make the amplitude appear higher, but the total power is actually balanced. Why does this happen? I'm not really sure, as you get the same thing on a trumpet for instance even if you mic it from the side, so you can't say that since the player is blowing through the horn, that it's the reason for the higher harmonics to be positive, so it's not due to the directionality of the instrument. I do however have to think about how the actual audio is generated. A player buzzes his lips, and then it's resonated, and amplified by the instrument. Now, I think it's fair to say that his lips would buzz differently as they go outward, than when they are recovering, or going back to their original position. I don't know why this isn't typically the case with a Trombone, but I can only guess that the size of the mouth piece, and the pressure, and frequencies involved are simply different. I can say that even with the same player going from a tenor trombone, to a bass trombone will get different looking results.

[PRobb]

Originally Posted by Dan

DAMN!

just kidding... I could be wrong, but it has to do the harmonic content. If there are more high frequencies on the + side of the polarity it will make the amplitude appear higher, but the total power is actually balanced.

Above and below the line is not frequency dependent. Just the plus and minus side of the waveform. Compression and rarefaction in the air, positive and negative voltage swings in a circuit.

[chrisrnps]

Originally Posted by Dan

DAMN!

just kidding...

Explication:

1) the act of making clear or removing obscurity from the meaning of a word or symbol or expression etc.
2) a detailed explanation of the meaning of something

"The idea and practice of explication is rooted in the verb to explicate, which concerns the process of "unfolding" and of "making clear" the meaning of things, so as to make the implicit explicit. The expression "explication" is used in both analytic philosophy and literary theory."

[joeq]

You see these waves all the time, especially with brass, and of course with synths anything can happen. As long as there appears to be the same 'area' above and below the line, I would not worry about it being DC offset.


from Wikipedia

When a periodic wave is composed of a fundamental and only odd harmonics (f, 3f, 5f, 7f, ...), the summed wave is half-wave symmetric; it can be inverted and phase shifted and be exactly the same. If the wave has any even harmonics (0f, 2f, 4f, 6f, ...), it will be asymmetrical; the top half will not be a mirror image of the bottom.

The following is totally over my head but for what it is worth I found this:

Asymmetric musical waveforms

It is possible to misunderstand the implications of Fourier theory and think that since waveforms can be represented as a series of sine/cosine components then, since each sinusoid component has symmetry, the result must also invariably be symmetric. This is a misunderstanding which fails to take into account the effect of the relative phases of components in Fourier representations. As a result of this we must also bear in mind that power-frequency spectra do not tell us the whole story.



The above waveform illustrates an example of a clearly polarity asymmetric waveform. This is composed simply of the linear sum of a cosine fundamental and its first four harmonics. The point here is that any waveform - symmetric or otherwise - can be represented using Fourier analysis as a set of sinusoidal components. However to preserve the information about the waveshape, the details of the relative phases are vital. In the above example, the cosine fundamental and harmonics are all in phase at the time = 0. Changing the phase relationship would maintain the same power-frequency spectrum, but alter the actual shape of the waveform.

[Dan]

I know, but I was still offering an expletive.

[Dan]

So it appears to be the presence of even order harmonics that causes this?

[Batchainpuller78]

so what now why are trying to get the look of our waveforms right???
become a painter not a musician then.

Is there something wrong with the sound? does it sound good? if it does who cares what the waveform looks like, that's just handy to edit

[Dan]

Originally Posted by PRobb

Above and below the line is not frequency dependent. Just the plus and minus side of the waveform. Compression and rarefaction in the air, positive and negative voltage swings in a circuit.

I'm definitely not saying the two are related in that way. I agree with what you're saying. In the example wave form, it looks to me like there's more HF content on the positive side of zero. I was digging from there as to why.

[monomer]

This is quite normal.
It is a proper energy distribution between above zero and below zero.
You will notive that the peak above zero is very high, but only for a shot amount of time.
The lower part is not very deep but lasts a lot longer.
As stated above, the area of both parts of the waveform are the same.

It has nothing to do with the harmonics being present or not.
It has to do with how the harmonics are arranged within the wave.
You can change the look (and energy balance point, the zero) of a waveform dramaticaly by changing the phase of harmonics.
It will still sound the same tho.