Looking For Advice From the Recording/Audio Gurus Here

[OldManC]

Hey guys, I realize this is a long shot but I'm looking for advice on some technical issues I'm having with some old recordings and I know next to nothing about this end of making music.

My old band recorded these tracks on a 1/4" Fostex 8 track in 1989/90. I recently had them digitized and have discovered these sort of squeaking sounds that pop up intermittently on different tracks. I'm not sure what they are or how they got there but I don't think they're part of the digitizing process (and they weren't there 23 years ago). I've clipped a few examples here. Any ideas out there on what might have caused these or anything I can do to remove the offending squeaks while keeping the rest of the audio in tact?


https://soundcloud.com/oldmanc/sets/squeaks-anomalies-on-old-8

[Pilgrim]

I listened to it twice but couldn't hear any squeaking. Maybe it was the speakers on my laptop.

What I have run into with older 1/4" tape is that there were originally some lubricants built into the tape.  Older tape has sometimes dried out and the tape may chatter slightly and vibrate as it passes over the playback head, causing a sound that may resemble a squeal. I don't have a solution for that other than to EQ out the offending frequency.

[OldManC]

Older tape has sometimes dried out and the tape may chatter slightly and vibrate as it passes over the playback head, causing a sound that may resemble a squeal.

That sounds like that could be it. A friend on Facebook recommended Spectral Layers Pro and I downloaded a trial version tonight after I posted this. It looks like I can go through with it and splice out the noise while leaving the rest of the sound alone. I have to dive deeper into it but I think it will work...

[Pilgrim]

Here's one bit of advice from my field recording - if you have to cut a specific frequency, cut it throughout the entire recording - don't bring the EQ in and out. 

If the EQ on that frequency is set the same all through the recording, the omission of that frequency really isn't noticeable.  But bringing it in and out sounds really weird.

[Granny Gremlin]

I am not familiar enough with open reel tape use to speak to degradation or potential noise/distortion from playback machine issues, but to me this sounds like a digital problem for the following reasons:

- It only happens at or around waveform peaks - why nothing in quiter or even 'silent' sections?  I'd expect tape degradation to not correlate with signal so much (but as I said, not so familiar with that).  This could also be distortion on the input chain of the recording process of course, but you say this was not there (from memory?) when first mixed.  I suppose it could be tape player electronics on playback when they were digitized, but in that case it is still the fault of the dude who did the job and a bit of a hair split.  The vibration over the tape head thing would also be more constant/random vs the signal wouldn't it?

- the nature of the sound is somewhat digital as well.  Not straight up converter clipping, which is very much more obvious (and inexcusable), but sounds a lot like when a DAT glitches out or my old sound card when it lost synch on mixdown (hasn't happened since I was using a PII with the very first commercially available USB interface).

- the glitches are so quiet (like Pilgrim, I had trouble hearing them until I switched to better speakers) that it sounds like someone else may have already made attempts at removing them.  This is not a strong point, but  a possibility worth mentioning.

- the audio seems to be rather compressed, even when just looking at the waveforms on Soundcloud, but it sounds like it too.  A clean vocal track will never be that narrow dynamicly, especially when belting it out like that first bit.  It could have been on the input chain (compressing the shit out of everything was very much in style in LA at the time), but if it was done after, especially if in the box with plugs and if one of those (multiple daisy chained compressor/limiters are all the rage now) was a brick wall limiter, then there's a potential culprit too.  Plugins or other DSP can leave artifacts that would not be as loud or jagged as proper clipping, analog or digital.

The only way to know for sure is to go play back the tape on a known good properly aligned deck and listen for it.  Was the deck used in the digitization process the same deck it was recorded on (maybe even yours)?  Did you perform the task (i.e. know exactly what was done and what was used to do it)? 

As for what to do about it, hard to say.  The problem is the DAT-like slide nature of the noise.  I'd start with a parametric EQ - something surgical and capable of extreme notch filtering.  You may need to cut multiple freqs or use a slightly wider Q or band to get the noise out, but it might not cut it.  I'd then try any sort of denoiser/pop remover you can get your hands on (e.g. for cleaning up digitized vinyl), but it's hit or miss with these and different ones work better on different types of noise. I have heard good things about Spectral Layers but have not tried it myself.

[OldManC]

Thanks for the advice and ideas! I downloaded a trial version of SLP tonight and with about 30 minutes playing with it I out three clips through it and changed the link above so there are three before and after clips. They're not perfect yet but I think I'll be able to make it work after a couple more days of working with it. I have 15 days on the trial so I think I'll be good to go!

[Pilgrim]

I went back and listened to the audio clip with a set of Sony MDR-V6 headphones.  I could then hear the problem.  Definitely NOT tape vibration, it's related to the sound peaks.  The section of the clips starting at 47 seconds is most illustrative...the peaks are steady there and the sound occurs more often.

I'd call it almost a clicking sound - but it's a digital artifact and I'm pretty sure it's caused by the way the software is capturing the audio. Almost certainly caused by overmodulation or inability of the computer to process the peaks properly.

A simple thing to try would be reducing the gain slightly (maybe 20%) and seeing if that eliminates it.  

One of the biggest changes I've had to make in switching from analog to digital recording is the way I handle gain and peaks.  In analog recording (usually metered with a VU meter), the goal was to get as much gain as possible without distortion, since it was important to maximize signal to nose ratio.  In digital recording I've found that it's better not to push max gain, but to bring it down a little to eliminate digital distortion, clipping and similar sound artifacts.  With digital signals I can always turn up the volume of a low gain signal, but I can't turn down distortion caused by excess gain in recording.

[Granny Gremlin]

Yes, digital recording is all about gain staging with a view to ensuring headroom on every input stage (converters, fx and summing channels, like groups and the mix bus).