100 Hz Peak in Noise Print?

[cubdukat]

I've been noticing on my vinyl rips that when I go to take a noise sample, most of the time it's the normal slope you'd expect from the RIAA curve. But when I take a sample from Philips/Deutsche Grammophon releases. I'll find a peak at around 100 Hz. Sometimes it's a small hump, other times it's noticeable.

I'm not overly worried, since the rip still sounds good, but I'm wondering whether there's something normal, and what could be causing it?

Like I said, it mainly happens with Philips/DG/London releases. Maybe it's something unique to those labels?

[Craig Maier]

Those brands of record were recorded in Europe. European (including English) power supply mains operate at 50 Hz (as opposed to ours here in the US which operates at 60 Hz). The recording equipment all uses full wave rectification to drive their amplifiers. Full wave rectification produces a ripple frequency on the power supply rail equal to twice the line frequency. In Europe, that would be 100 Hz which inevitably bleeds into the recording, so that is what you are seeing. Just bring up the Notch Filter and set it for 100 Hz, and the 100 Hz noise will be gone after you run it.

Craig

[Craig Maier]

As an aside to this, you will sometimes find recordings that contain 120 Hz noise if they were recorded in the US (or other countries that have a 60 Hz power grid). The reason for this is the same mechanism as stated above for the 50 Hz situation. The solution is the application of the Notch Filter set to 120 Hz which will dramatically attenuate that noise signal from your recording.

Craig

[cubdukat]

Thanx. BTW, this is a screen grab of what I was finding. This one was actually from a 12" of a song called "Tapdance" by David Foster. It was an American pressing on Atlantic Records.

[Craig Maier]

It's hard to tell if that is a 100 Hz or a 120 Hz noise. You can use the spectrum analyzer (view menu) using a high resolution mode to determine its exact frequency. Nonetheless, whether its 100 or 120 Hz, the Notch filter should knock that noise signal out of the recording. btw - it really does not matter where a record is pressed, only where it was recorded, mixed and then mastered (which would have been Europe in the case that you presented). If you are unsure, first try notching at 100 Hz. If that does not work, re-try at 120 Hz. It is going to be one of those two frequencies that you are dealing with.

Craig

[Craig Maier]

Here is how I approach that sort of noise. I bring up the Notch Filter and set it for 0.1 Octave. Next, I switch it to "Slot" mode. Next, I set the frequency for 100 Hz and preview the file. I turn the gain to a high setting on my audio system so that I can hear the noise (only the noise will be heard in slot mode). Then, I vary the frequency control up and down around 100 Hz until I find the maximum peak loudness of the noise. After that is found, I then adjust the Octave control to the smallest possible value without losing the sound of the noise. Finally, after all these settings are in place, I switch the Notch filter over to normal (non - slot) mode. Preview it and then Run the filter. Noise is then gone.

Craig

Same process is used for 120 Hz Noise, except 120 Hz is the setting that I start with.

[Marc Hildebrant]

Interesting,

I have done that the opposite way. Turn on Notch filter and either listen of watch the frequency spectrum for the 120 Hz or 60 Hz tone to go away with the use of the filter.
I like your method better...

Marc

[Craig Maier]

Hi Marc,

Your method should work just find too. The spectrum analyzer has the advantage that you can click on the spectral 'spike' with the mouse and get an accurate reading of its frequency without guessing. Of course, you need to have the spectrum analyzer set for a high resolution mode (high fft count, etc).

Craig

[cubdukat]

As it turns out, the preamp I was using was cleared of causing the problem. I got a new Pluto preamp this weekend, but the hum persisted. Turns out it was the computer itself that was causing the hum because there's a ground loop somewhere, so now I have to figure out how to stop it. In the meantime, I've added 60Hz notch filtering to my workflow.

[Craig Maier]

Consider using an audio isolation transformer between your audio source and your computer sound card input. That should break your ground-loop.

Craig

[cubdukat]

I'll try that. I may have found one part of the problem, though. When I installed the mobo, I just put the I/O shield in and didn't pay attention as to whether it was making actual contact with the mobo, so I'm going to attempt to re-mount the mobo after I've bent out the tabs on the shield accordingly. Hopefully that will solve the problem, because it also extends to the Fast Track Pro as well.

That being said, apart from the hum, my needles drops have improved 100 percent. If I lick the hum issue, I'm home free...

[Craig Maier]

Here's a couple more suggestions. Plug everything (preamp, turntable, computer, etc) into the same outlet strip. Do not use different outlets in the room for these items. Use a 16 AWG ground wire between the turntable chassis and the preamplifier chassis. Similarly, use another 16 AWG ground wire between the preamp and the chassis of the computer. Keep these ground wires as short as possible. As you alluded, make sure that the mobo is grounded to the computer chassis in numerous places. And, of course, consider using an audio isolation transformer between the output of the preamp and the line input of the computer (as mentioned earlier).

Craig

[cubdukat]

Found a temporary solution for my ground loop problem. Actually, two solutions, one hardware and one software:

1. The hardware solution was that I bought a cheap ground loop isolator off of Amazon, and that seems to have cut the hum way down. Unfortunately, bass is not what it was before that, so I still have to experiment with EQ. In its defense, though, the surface noise level has also dropped significantly.

2. The software solution was I created my own "Humbuster" preset for Harmonic Reject, followed with Spectral Subtraction noise printing. The advantage here is that for the most part, I'm getting excellent needle drops, with beautiful bass and clear highs, and the hum/buzz is all but gone.. It's just inconvenient as hell

Right now those are how I'm dealing with this ground loop until I can actually get a better power supply. I got a cheap 600W Micro Center PSU to replace an 850W Corsair that lasted almost ten years without issues, and I'm paying the price for it now.

Would applying an RIAA curve a second time solve my bass issues?

[Craig Maier]

I would not recommend applying the RIAA curve twice. That will make a mess out of the audio spectral balance. As for the loss in bass, that is because the audio isolation transformer is probably of very low quality. A good audio transformer will remain flat down to 20 Hz and up to 20 kHz. It sounds like the transformer you purchased is not capable of responding to either extreme ends of the spectrum. Look on the internet for a professional quality audio isolation transformer and that should solve the problem. I have some old UTC transformers that cover the entire audio spectrum with no bass loss, but they are from the 1960s. Not sure who makes good ones today.

Craig

[cubdukat]

That was probably it. It only cost me 10 bucks on Amazon, 15 with shipping. I decided to take it out of the loop and do the software Humbuster thing until I can replace the PSU. It doesn't eliminate it entirely, but it does reduce it substantially, and I still more or less have my full frequency range. I've only had it a week, so it's still returnable.

One other thing, and this might be better in another thread, but wouldn't Spectral Subtraction also work for removing things like hum/buzz? I've fallen in love recently with that method.