What is causing these big dips?

I actually record LPs in my listening room with a Macbook Pro. But then I move to Windows 10 to edit and export. For some reason, sometimes I get these really drastic peaks and dips, but they seem to not affect the sound. They do effect the use of filters on the samples. Reflect artificially high and low peaks. How do I get rid of them with going all the way down to sample view and writing them smooth? Please see the attachment. This is my first post. Kinda noobie.

Wow, that’s dramatic.

If you record the LP a second time, do you get those dips at exactly the same place in the music? I’m guessing they don’t.
What turntable are you using and how is it connected to your Mac?
Any special reason why you posted this on the Windows forum board rather than the Mac board? Have you looked to see if these blips are also present on the Mac?

thanks. Yeah they are on the MAC too. It’s a Thorens TD 160 with new Stanton Cart. New cables, niceley rebuilt. Since I’m editing on the PC I just put it here. Not that much diff I guess. I haven’t tested to see if they are in the exact same place on a re-record of the LP. I guess I should. I can tell you that they happen exactly the same way on other albums, but yet, some albums don’t do that at all. I am using a McClelland turntable preamp directly into the laptop, no receiver involved.


Nope. Analog/RCA Y chord into Laptop built in input. Hi-end cables no longer than necessary. Been using this setup a while without the problem. When it happens it’s 3-5 times over the course of an album. Some records don’t do it at all. I really don’t know what I am looking at here. but the issue doesn’t seem to affect the playback, or at least it’s insignificant and maybe that’s supposed to happen. I don’t understand the waveform printout that much. But enough to remove clicks and clipping and run the enhancements like normalize etc. But this makes it much more difficult and time consuming. Right now I have to select just after and before these “Waves” to enhance and basically leave them out. Could things like the AC power in the house, grounding or other interference cause something like this? To me it looks like something I should be hearing, but don’t. Wish I knew more about it. I have several hundred albums to do yet.

If you apply equalization to remove infrasound, the “big dipper” should disappear …
No-Infrasound ''curve''.png
No-Infrasound.XML (187 Bytes)

Does your Mac look like this:

That thing on the left is a high-volume Stereo Line-In and I’ve been using it for Mixers, Turntables Preamps, etc for years. If you have a newer MBP, you have a single socket intended to do everything. I would bet significant chocolate that’s what’s causing your thumps.

If you have a big enough sound system, those will appear as thunder, trucks going by or earthquakes. On a normal or smaller sound system, you won’t hear them at all.

That custom filter should get rid of them, but it’s best to not make them in the first place.

On later Macs or Windows machines this Behringer UCA-202 interface has been found to work well.


Even on a huge sound system you won’t hear it. Look closely at the time scale - it’s about 1 Hz.

Normally audio signals should oscillate around the 0 volt line (the vertical middle of an Audacity track). When there is total silence, the signal should be a flat line in the middle of the track, and as a signal increases the waveform should oscillate up and down by a roughly equal amount in both directions so that the average remains in the middle.

There’s a fault condition called “DC offset”, where the average level, (and the level of silence) is not in the middle, but slightly offset up or down. This fault is due to a small DV voltage being present on the signal. That is not what is happening in your case, but it perhaps helps to visualize what is happening:

In your screenshot, just after 8:52.5, the average level starts to drop rapidly, and continues to do so for about 1/4 second., then rises for the next half second, then falls back to an average around 0. The entire cycle lasts about 1 second. The way that it overshoots and gradually settles down at the end looks like an analog problem, not a digital thing.

As Trebor wrote, it should be very easy to “fix” the recording just by filtering out that extremely low frequency pulse, but it’s worrying that it is happening in the first place. That is not normal, it’s a fault, and my guess is that it is a hardware fault somewhere.

That’s going to make it tough to pin down where the problem is.

The way I would approach it is to try making some half hour recording of “silence” with everything set up as normal, and everything turned on, but with the turntable disconnected from the preamp. It’s important that everything else remains exactly the same as if you were recording an album. By changing exactly ONE thing at a time may show where the fault lies. If the problem occurs with the turntable disconnected, then we have ruled out the record, cartridge and turntable as the source of the problem.

And something you can do independent of the hardware, do all of those disturbances look the same? Do they all go down first and then up? Are some of them backwards? Do they alternate?


This is what you get if you pass a huge pulse through a large smoothing filter and add it to an audio signal. Does this look familiar?

Do you own one of those electric insect zappers?
Have there been any power outages recently?
Do your household llights ever dim of flicker for no reason?
Is it “the rainy season”?

I haven’t tested to see if they are in the exact same place on a re-record of the LP.

I suggest you do that. You don’t have to re-record the whole record, just the part where the glitch occurred.

I have two guesses - It’s either a defect in the record itself, or a mechanical shock/vibration getting to the turntable. For example, if you have wood floors, just walking across the floor can transmit vibrations to the turntable. Some vinyl enthusiasts go to great extremes to isolate their turntables.

I mostly suspect an external shock/vibration. If it was “normal” record warp with would happen once per revolution, or at least for several revolutions in a row where the warp was the worst.

The waveform you showed isn’t [u]clipping[/u] so you should be able to filter it out. And you should filter it out for a couple of reasons - It may get through your amplifier to your woofer/subwoofer where it could cause clipping or other distortion & “stress” on the amp, and because if that’s the highest peak in your recording it will limit the amount of digital volume boost you can apply before clipping (you can go louder without that unnecessary subsonic peak).

That could do it, but it would need to be a pretty big mechanical shock wouldn’t it to make a peak that big?

I wouldn’t mind knowing the Mac version. It could be the “One Size Fitz All” connection trying to figure out whether or not to switch on Microphone Battery.


That could do it, but it would need to be a pretty big mechanical shock wouldn’t it to make a peak that big?

Yeah… I don’t really think it’s from walking across the floor. But, I have heard sounds through a turntable caused by walking across a floor (at high gain/volume levels). And, I’ve read about some people getting feedback from the speakers through the floor to the turntable.

It does look “analog” to me and maybe someone is touching/bumping the turntable. …Maybe he lives here in California! :smiley: :smiley:

I don’t know anything about that particular turntable and it would also depend on the preamp so I don’t know how sensitive the setup is.

Wow so many great responses! Thanks. Yeah - that’s my MBP 2009. Figured the SSD and just the tiny fan would be the least noise. Downloaded the filter xml. I was trying to find a way to remove them after the fact and that oughta do it. Like the idea of recording a half hour of silence with TT detached. Should prove something, but what to do about it? The Thorens is a 1975, but kinda sat for about 15 years. Replace some caps maybe. Both of my systems can do sub 30, but it is a very short pulse. Might be easier to watch the sub move than it would be to hear it. Never had any problem with the analog McClelland. Question: If I use a USB preamp is the DAC done in the preamp and not the MBP? Just always thought keeping the sig analog going in was best and eliminating any USB drivers? Last question: Although it’s inaudible, the Audacity recording meters are always bouncing a little when the TT is live but nothing is playing. Is that normal or should there be complete silence? It’s always below -36 but concerns me. Thanks again.

Yeah, they are always the same, some are bigger and peak at the clip line.

Not quite Steve. They are always equal up and down.

MBP 2009.

So yours are cousins to mine. Are you plugged into the connection with thin circle and two black arrows? 15" or 17"? The 13" only had one connection and you had to manage it in System Preferences.


Pre-Amp FAIL - Sorry to bother everyone with such a fundamental issue. I guess my fancy British Pre-Amp is Junk. Might not have been, but is now. I realize there’s probably no pre-amp turntable combo that is completely silent, but of course this is unacceptable and I have about twenty LPs that will need redone to a higher standard. What is the most quiet model I can expect in the 100-150 dollar range. USB or not, Tubes or not? Thanks to all for sending me in the right direction.