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Distorted sibilants

S

SFM-Ptgal

The title is not for a broadcast processor issue... It's for my Harris cart recorder.

While recording jingles taken from the internet onto carts I noticed that sibilants come quite distorted while other frequencies are well balanced. That happends with different tape brands. The machine it's obviously old. Is this typical from dried out caps?...

Pedro
 
Assuming the "jingles take from the Internet" are of sufficient quality, it almost sounds like it's a phase issue.
 
If the recording bias oscillator has gotten weak , or the record head is too worn, you'll have this problem.
Someone may be able to tell you what the voltage should be for the recording oscillator.
A scope will be very useful to see what the output looks like.

On the other hand, if the bias is set too high, there will be partial erasure occurring during recording, and everything will be dull sounding
on playback, but previously recorded carts will sound OK.

Do carts recorded elsewhere sound OK?
 
Tom Wells said:
If the recording bias oscillator has gotten weak , or the record head is too worn, you'll have this problem.
Someone may be able to tell you what the voltage should be for the recording oscillator.
A scope will be very useful to see what the output looks like.

On the other hand, if the bias is set too high, there will be partial erasure occurring during recording, and everything will be dull sounding
on playback, but previously recorded carts will sound OK.

Do carts recorded elsewhere sound OK?
Click to expand...

Despite the age, both heads are quite nice (perhaps replaced b4). I have the cart recorder manual, I don't have a scope. Yes, carts recorded elsewhere are ok.
Should I tweek the bias keeping in mind the current position?
 
Yes, but do at least measure the AC voltage for reference, you never know just how touchy an adjustment potentiometer is going to be.
Average bias frequencies are 30-50 khz, so hopefully your meter reads AC that high.
Even if it's not accurate at that frequency, you'll at least be able to set it back to the same reading.
 
What is a cart?? ??? Seriously, What kind of tape are you using? Hot tape, MXi, etc? True story: A friend and I were rebuilding a FM studio circa 1994. They were dumping all carts to go computer (digilinks IICR). They had ten or twelve ITC Delta's and some of the older triple decks. The owner wanted them thrown away. We took them all but one which had some bearing issues. That last triple deck we used for an experiment. At around 2 a.m. when all was clear, my buddy dropped the ITC from a third story window to the concrete below. We brought the machine back up and it still worked. Today, broadcast equipment is not made the same way as the good ole days ;D
 
How big of a dent did it make in the sidewalk?

That's about the highest serviceman's calibrated drop I've ever heard of.

Did it fix the bearing issues? Or was it still noisy?
 
From memory--it's been a while! If you can run an audio oscillator into the record input while monitoring the playback output, run a 10khz tone in & adjust the bias level until the 10hkz level peaks & then continue clockwise with the bias adjustment until the playback level drops 1.5db from the peak. Your bias setting should be correct at that point. If the distortion on the highs is still there, you'll need use a test cart to verify that the frequency response on playback is correct, then using the audio oscillator, note the playback level at 1khz & adjust the record high frequency equalization until the playback level at 10khz matches 1 khz. After achieving that, sweep across 50hz to 15khz and hopefully the response will stay within 2db at all frequencies. If you do all of these steps & the machine meets the above numbers after adjustment, I'd expect that the sibilance distortion will be gone. You can do a quick pre-test to see if this is the problem by record voice at an average level & then speaking a long SSSSSSSS at the same level as the voice. When you play it back, watch the VU meters...if the SSSSSSSS shows a higher VU reading than the average voice level, odds are excellent the above will lead you to a resolution. If you don't have an audio oscillator, programs like Adobe Audition can generate tones (in that case, Generate>Tones from the File, View, etc list). Good luck...maybe one day you'll win a prize for being the last person to still have a working cart machine :)
 
BobOnTheJob said:
From memory--it's been a while! If you can run an audio oscillator into the record input while monitoring the playback output, run a 10khz tone in & adjust the bias level until the 10hkz level peaks & then continue clockwise with the bias adjustment until the playback level drops 1.5db from the peak. Your bias setting should be correct at that point. If the distortion on the highs is still there, you'll need use a test cart to verify that the frequency response on playback is correct, then using the audio oscillator, note the playback level at 1khz & adjust the record high frequency equalization until the playback level at 10khz matches 1 khz. After achieving that, sweep across 50hz to 15khz and hopefully the response will stay within 2db at all frequencies. If you do all of these steps & the machine meets the above numbers after adjustment, I'd expect that the sibilance distortion will be gone. You can do a quick pre-test to see if this is the problem by record voice at an average level & then speaking a long SSSSSSSS at the same level as the voice. When you play it back, watch the VU meters...if the SSSSSSSS shows a higher VU reading than the average voice level, odds are excellent the above will lead you to a resolution. If you don't have an audio oscillator, programs like Adobe Audition can generate tones (in that case, Generate>Tones from the File, View, etc list). Good luck...maybe one day you'll win a prize for being the last person to still have a working cart machine :)
Click to expand...

An update... I've testing the cart machine with other material than the one I collect on the internet. It became quite bearable. I had to adjust the console output to peak around 60% otherwise the carts will have broadband distortion. Regardind the SSSS... I did d-essed the audio on a dsp plugin. It worked quite well. I think I'll keep it this way for now...
I'll never be the last person to have a cart machine... There are those who collect old cars... I d'love to collect old broadcast gear. The dream came true about a year and a half ago... Old but no need for a variac ;D
Just to remember:
http://www.youtube.com/watch?v=Uoxc9wlqjd8
I'm cooking another video (only harris stuff and with day light)...
 
boiseengineer said:
Seem to remember that when setting the bias the record level on standard cart tape it was done at -20 dB.
Click to expand...
You may be right, but I know I've done it at 0 level with success as well. Using the VU meter built into the ITC's at -20 would make it necessary to guess where the -1.5db point was, whereas at full level it can be read with precision. Perhaps different cart machines had different preferred methods? In my case, every station I care for has stopped using carts since about 2000 and I couldn't be happier!
 
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