MacBook Pro (OS X El Capitan 10.11.4)
Source: Line out from tape player to line in on laptop
I’m trying to digitize a set of spoken word audio cassettes. They are quite old and not professionally recorded, so vary in quality. I’ve had success with all apart from one side of one cassette. When playing back the recording of this side, it contains lots of high frequency clicks. This only happens when the voices are present, ie. it’s fine when people are not talking. I’ve tried recording at a lower volume but the same problem exists.
The strange thing is that when I listen to the cassette tape directly via the tape player (using headphone port) there is no such interference. Additionally the other side of the tape (and three other tapes I’m recording) do not have this problem either.
Can anyone advise what this problem might be due to and how to fix it? Alternatively is there some post-processing that can be done to remove the interference?
I’m happy to post a short piece of the recording to provide an example if that would help.
Is it really Line-In on the laptop? Do you have a 15" MBP from about 2012? Does your connection look like this:
If it’s a more modern MBP, then you don’t actually have a Stereo Line-in. You have a headset connection similar to Windows machines. If you have an older 13" MBP, then you do have a Stereo-Line-In, but you have to switch to it in Mac preferences.
Your symptoms are for someone trying to connect a tape machine to a Mic-In of a headset connection. Those can overload creating pops and clicks and there isn’t much you can do about it because the volume controls take charge after the overload already happened.
Are your blue waves really tall and do they sometimes go all the way up and down on the timeline? Do they have little flat spots on the peaks? All those are indications of an overload condition.
If you watch the sound meters in Audacity, do they go all the way up to red during that one tape?
Yep, it’s a MBP like the model pictured that has a separate line-in, so I assume we can discount the overload already happening. I appreciate the clicking does sound like overload but the blue lines do not indicate this and there’s no red shown with the “show clicking” option on. Additionally, I’ve tried reducing the input recording volume but the problem still exists. I’m especially confused as it only happens on one side of one cassette tape! I’ve followed exactly the same procedure with the others without issue.
Do you get the same waveshape tiny spikes in the same place in the performance if you play over the tape multiple times? Then it’s burned in to the show. If the little spikes move around then It’s a mystery. I don’t know of a tape mechanical failure that can cause sharp clicks like that.
It would have to be a local, mechanical tape failure otherwise all the tapes would do it.
I can do magic… The humidity was much lower during the clicky tape and the anti-static coating was worn off. But that’s really pushing it.
Just to cover it. You did flip the tape over more than once, right? One pass at a problem is an anomaly or artifact. If it happens repeatedly, that’s a problem.
The only thing I can imagine is that the headphones output from the tape deck has a high cut filter that masks the high frequency spikes enough to render them inaudible.
Are you listening with the same headphones to the deck and to your Mac?
What happens if you low pass filter the recording in Audacity at 5 KHz or so?
What happens if you record from the headphones output of the tape deck?
Could you post a small sample? (<10 sec. mono, 16 bit 44.1 KHz should do fine) In the sample we could maybe see if the high frequency peaks could be inaudible in an analog tape deck, but somehow create audible interference in the digital copy.
All grand ideas, but the poster flips the tape over and the problem goes away. And that was very specifically the condition I asked about. As I see it, we have enough information for a mystery movie plot, but not enough to solve the problem.
So if you re-record the tape are the clicks in exactly the same place as before?
This is a long shot but go to the system Sound Preferences, “Input” tab and ensure that any “Use ambient noise reduction” checkbox is unchecked. You may have to select the built-in internal microphone to make this checkbox visible.