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Topic: My waveform looks funky (Read 7390 times) previous topic - next topic
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My waveform looks funky

anyone know why my waveform looks like this when i record from vinyl?


see how the bottom half of each channel has more prevalent peaks than the upper half?? i don't really know what this means; can anyone explain it? i have never seen a waveform like this so i just wanna know if it's bad and if anything can be done to make it normal.

My waveform looks funky

Reply #1 –
What is your signal chain? Do you have the option of attenuating the input signal leve.l? It certainly appears to be too high. What does Analyze/Statistics say about DC offset; is there anything substantial?

If this is what you get from any and every LP, it is not normal. It looks like there is an offset and the positive side is clipping (possibly before the soundcard). There also appears to be soundcard clipping on the negative side, but not so extreme. If you zoom in very close, so the individual peaks are clearly visible, are many flattened?

Non-symmetrical forms are not at all uncommon, and are perfectly normal on speech, but not so much on music. You can see that on some lower level parts of your screenshot, at beginning and end of track, the waveform is more symmetrical.

My waveform looks funky

Reply #2 –
here is a screenshot of the amplitude statistics:


I'm using an Audio Technica AT-PL120 with a built-in preamp connected to line-in on a VIA Envy24 sound card (Chaintech AV-710) with an RCA to mini-stereo adaptor. I record in Audacity at 96khz/32bit with the input level as low as possible because if i move it any higher then it clips. right now if i zoom in there is very, very minor clipping... no more than 5 samples at a time, so it's unnoticeable. now that I go back and look at my other recordings, the same peak imbalance happens on pretty much every LP but i didn't really pay attention to it until this one (Silversun Pickups - Carnavas). even quieter records like the one I just recorded by Boston also have the same kind of unsymmetrical peaks but there is much more headroom. here's a screen shot of Boston's first album: http://i18.tinypic.com/2it0bph.png

unfortunately the built in preamp doesn't have a volume control so this is the quietest it's gonna get.

My waveform looks funky

Reply #3 –
I'm not an expert with Vinyl, so take this as an oppinion:

It could be that the nail of the cardtridge is a bit offset, so the peaks on one side can't move enough.

Yet... i assume that with a professional turntable that would hardly be the case..

My waveform looks funky

Reply #4 –
It looks like somewhere in your amplification chain one of the stages is exceeding its maximum amplitude. It's not unusual for an amplifier to limit at a lower level for one polarity than the other.

You may need to attenuate the signal between the preamp and the sound card.

My waveform looks funky

Reply #5 –
This Envy 24HT-S is the DSP chip for multimedia/gaming applications. It functions in the digital domain, after the A to D converters. By then it is too late to handle any signal level problems.  There is no analogue level control on the soundcard. The correct level must be obtained in the analogue domain, before the signal is fed to the soundcard.

As far as the software control panel goes, there is no calibration so I can't guess whether there is any DSP amplification, or if this card works like almost all professional audio cards -- it can only attenuate. If the later, the proper way to record is with the faders at the top. If it isn't correct with that setting you are throwing away bits; your signal need more adjustment in the analogue domain.

Like all gaming/multimedia cards, this one resample to 48kHz. If no way is provided to bypass the DSP (the Envy chip), recording at 48kHz will get you the best audio quality. However, whether the A to D converters will work at other than 48kHz is improbable, so it is extremely likely that 48kHz is it.

From the Via Technologies web page:
Key Features

Sound Quality
» Analog 20-bit/48KHz I/Os
» Digital I/Os supporting 24-bit/192KHz I/Os
» Bit-for-bit accurate transfers

Why ever are you recording in Audacity when you have Audition?

My waveform looks funky

Reply #6 –
Almost all envy24 based card can do 44.1 Khz sampling rate. So unless you know for a fact that this card doesn't, i'd think twice about your claim.

My waveform looks funky

Reply #7 –
Do you see the specs I put into my post? They are from the semiconductor manufacturer's website. That is what the manufacturer says the Envy 24HT-S does on analogue. It handles digital passthrough without resampling, but not A to D or D to A.

Therefore that restriction applies to any card using the chip unless,perhaps, there is a bypass to and from the codec that doesn't go through the chip. That method of I/O would not have any level control or the ability to do any other processing that the Envy chip handles, and would probably not resister on the soundcard VU meters.

Those same specs on also supplied with the soundcard. They are up front about it because they probably don't want to get sued, as Creative was, about their cards' resampling.

My waveform looks funky

Reply #8 –
The Envy24 isn't a 'the'.  There are a variety of them with different specs for different uses.

My waveform looks funky

Reply #9 –
so what can I do to fix this? do i buy another phono preamp and not use the internal one?

My waveform looks funky

Reply #10 –
Both cartridges and phono preamps vary. The greater differences may be between cartridges rather than between phono preamps. Without having good specs on both the cartridge and phono preamp, you cannot tell if another phono preamp will solve the problem except by trying it.

If we assume the problem is at the soundcard input -- the input signal is too high -- and not that the phono preamp itself is clipping (not a very likely situation), you need to reduce/attenuate the signal level between the phono preamp output and the soundcard input. This is the normal remedy.

The usual solution is a small mixer or a line level preamp placed after the phono preamp, before the soundcard. A "passive" volume control would also do the trick, but is not the optimum approach. Generally speaking, it is easier to have a variable control so you can set the level as you wish, but it is also possible to get by with a fixed attenuation (once you determine a suitable attenuation).

If you have some electronics project skills, it would be easy to make a volume control or a fixed resistor network; buffering the output would be best. If you have no electronics experience, a used mixer is probably the least expensive option.

My waveform looks funky

Reply #11 –
I'm with [JAZ].. this looks like an alignment issue with the cart/tonearm, and not anything with levels.

You can easily test that by grabbing a DVD player, and playing a CD into your analog inputs, recording it, and seeing if it shows the same issue.

My waveform looks funky

Reply #12 –
Assuming the CD output is reasonably matched to the soundcard input. I've seem more clipping from CD player  than from phono preamps due to higher CD player output. However, the output is not likely to be so high that a recording with good dynamic range won't look reasonable over most of its duration.

My waveform looks funky

Reply #13 –
Update:

I got a new sound card, the HT Omega Claro 7.1
It has much better levels -- it doesn't clip anymore, and I can put the line in at a mid-to-high level without it clipping.
However, my waveform still looks the same with the bottom peaks more pronounced than the top. So it's obviously a problem with my turntable.
Quote from: Cyaneyes on
I'm with [JAZ].. this looks like an alignment issue with the cart/tonearm, and not anything with levels.

How do I fix such an alignment issue? I balance my tone arm all the time. what else can I do?

My waveform looks funky

Reply #14 –
Your problem could be related to poor antiskating adjustment
The name was Plex The Ripper, not Jack The Ripper

My waveform looks funky

Reply #15 –
Quote from: JeanLuc on
Your problem could be related to poor antiskating adjustment

i've really tried everything when it comes to the knobs. i've tried setting the weight to everything between 1g and 3.5, and the antiskating to the corresponding weight as well as all the way up to 7. i also tried messing with the height adjustment and that didn't change anything.

My waveform looks funky

Reply #17 –
Quote from: Madman2003 on
Almost all envy24 based card can do 44.1 Khz sampling rate. So unless you know for a fact that this card doesn't, i'd think twice about your claim.


The Envy24 HT-S (unlike e.g. the good ole' "pure" Envy24) does not feature a switcheable MasterClock for its analog input ... it features a sample rate converter instead (maybe that's what the "S" stands for) and records at a fixed fs of 48 kHz.
The name was Plex The Ripper, not Jack The Ripper
 

My waveform looks funky

Reply #18 –
My early recordings, starting with a new cartridge, had a different, but quite obvious problem. There was a good bit more noise, along with more clicks and pops, on the right channel. This applied to about 8 or 9 out of 10 LPs -- but not all of them.

I buy most of my LPs from thrift stores. Since this problem didn't seem to effect quite all of them (still don't know why), I believed it must come from poor cartridge alignment  in the former life of the disk. I figured it must have been something like poor bias adjustment and the physics favored it more likely being out in that direction.

On day I was peering at the stylus with a jeweler's loup to ascertain the effectiveness of my cleaning attempts and noticed that the stylus was definitely canted off to one side. Closer inspection showed me that the cantilever was bent. I had looked at it under the lens before. While I never noticed the problem before this viewing, the evidence of my recordings strongly suggests the cantilever was always bent.

Interestingly enough, a replacement stylus played the same LPs without any sign of the former problem, indicating no permanent damage to the LPs.. Since I record for transfer to CD-R, I had plenty of evidence that my new recordings of the same LPs sounded the same after declicking. I just had a lot less declicking and NR to do with the new stylus in place.

The point is, something mechanical could easily enough be causing your problems without the source being immediately obvious.

A complete, properly done, setup and alignment seems to be the next step.