Tape noise

[rayc]

Hi Folks,
I've been uploading old 4 track cassette recordings to computer for some tweaking & archiving to CD.
I've noted that some, not all, of the tapes have an interesting/annoying noise that isn't, as far as I can determine, part of the usual background tape noise.
The noise is low EQ & it that come up just before something recorded on the tape becomes audible. For example prior to a sax solo the background noise is tame and in line with what is acceptable give the NR built into the unit BUT just prior to the sax the low EQ noise comes up quite loudly. It's then masked by the sax solo & reappears after a pause in playing & just prior to the resumption of the solo.
This is more obvious if I've had to digitally amplify the piece but the oddity for me is that, even when amplified/normalised etc, the noise come jsut before the recorded musical signal NOT in the pauses.
Any diagnosis, prognosis and therapy?
I can provide a sample if this seems left field and beyond anyone's ken.

[Beck]

Could it be pre-echo from print through?

[The Ghost of FM]

If dbx type II noise reduction was involved in this equation, that might explain the noise characteristic as what's been described in rayc's post was a common characteristic of solo instruments.

dbx type II NR cuts off its low frequency processing at 100Hz because of the lack of linear response of low frequencies on many cassette decks. The pumping effect can become noticeable at the crossover point because of the level differences between what the unprocessed and processed levels are and especially so on music parts that were percussive by nature.

dbx type I, professional works down to 50 Hz and reducing this annoyance by a much wider margin but was only designed to be used on open reel recorders, running at 15ips which offered more linear low end frequency response.

You might be able to minimize this effect by recalibrating the Portastudio by tweaking the internal repro levels but if there is print through effects on the tape as well, as Tim suggested, you may be better off isolating those events in the digital realm and creating a level change envelope for the specific events to reduce their audible presents in the mix.

Cheers!

[MCI2424]

Originally Posted by rayc

Hi Folks,
I've been uploading old 4 track cassette recordings to computer for some tweaking & archiving to CD.
I've noted that some, not all, of the tapes have an interesting/annoying noise that isn't, as far as I can determine, part of the usual background tape noise.
The noise is low EQ & it that come up just before something recorded on the tape becomes audible. For example prior to a sax solo the background noise is tame and in line with what is acceptable give the NR built into the unit BUT just prior to the sax the low EQ noise comes up quite loudly. It's then masked by the sax solo & reappears after a pause in playing & just prior to the resumption of the solo.
This is more obvious if I've had to digitally amplify the piece but the oddity for me is that, even when amplified/normalised etc, the noise come jsut before the recorded musical signal NOT in the pauses.
Any diagnosis, prognosis and therapy?
I can provide a sample if this seems left field and beyond anyone's ken.

Check the condition of the cassette. Sometimes the felt backing wiper becomes loose or is gone altogether. Sounds like the tape is not in intimate contact with the heads and is wandering in and out. Wind and rewind the tape completely and see if it gets better. Packed cassettes do strange things. Firstly, demag and clean the entire tape path for chuckles.

[A Reel Person]

(as discussed on another thread), which would be like a fuzzy 'bwoww' a split second before & after any percussive or stacatto instrument sounds.

This may also represent 'dbx tracking errors' due to different setups on different decks, i.e., old tapes from former porta models being played on newer contemporary models & the relative differences in calibration between the two machines, (thx Tim Gillett).

Unfortunately, there's no good way to remove dbx pumping noise on previously recorded tapes, 'cept to try to make sure your current porta is properly aligned and calibrated. It was mentioned in another post that in dire circumstances you may consider 'detuning' your current porta to 'read' the older tapes (dbx decoding levels) properly, but (IMO) I'd not go there, lest you end up with twice as many calibration issues than before. It could be a nightmare for all but the best DIY'er.

It's preferrable to try & avoid 'dbx pumping' at the source and record-side of the equation, (also previously discussed), but that's not relevant to your problem with 'archive tapes', most of which I sure were recorded years ago.

[Tim Gillett]

Hi rayc,
It's hard to be totally sure about what it is without actually hearing it. Can you load up a sample for us? Sounds like it's in digital form already.

Cheers Tim.

[rayc]

Hi Folks,
Some very interesting ideas & possibilities.
Here is the sax solo in question. I've removed any EQ & compression it had in the digital domain. Naked the noise actually isn't masked very much at all.
hi-fi URL: http://www.soundclick.com/util/getpl...d=4803357&q=hi
Downloading the MP3 from the 1st link in my signature will get you a somewhat better degree of quality compared to the streamer from the link above.
The tape is fairly new as is the sax part of the recording - I had uploaded the 4 tracks to comp. & then manths later mixed down to tape to record the sax alongside for later upload & incorporation into the unmixed work in cakewalk proaudio 9.3.
Recorded onto a chrome 10 min tape (TDK SMX10) using a yamaha mt100 with dbx. As you can hear between phrases the noise level is quite low BUT just prior to & through the playing it's the pits.
Even a precise EQ cut suggestion might help.

[cjacek]

Please don't take my view seriously as I may not know what I'm talkin' about in this instance but to me it sounds like AMP noise coming in with the sax, which was possibly originally recorded with the instrument. Perhaps a grounding issue ?

[rayc]

C'mon folks - sample provided.

[rayc]

cjacek,
You may well be correct. I'm confused though as to why there is no noise between sax phrases. Any idea? It was recorded with the mic open for the entire passage.

[Slowrider]

I had something similar happen a few yrs. ago recording my 12. Hasn't happened since. Have NO idea how I "fixed" it.I thought I could hear some Breath noise on the sax; but I'm old and deaf in o

ne eye, so what do I know? Maybe overdriving the mic?

[cjacek]

Originally Posted by rayc

I'm confused though as to why there is no noise between sax phrases.

...and that's where it gets puzzling. I listened to the cut several times with my AKG studio headphones and it does sound like amp / grounding issue noise but why it appears only when the sax comes in, is beyond me ... I hope someone can shed some light on this phenomenon.

[cjacek]

OMG, I think I got the answer, at least a part of it! Slowrider said something about hearing "Breath noise" on the sax and this gave me another thought .... Did you by any chance use dbx noise reduction when recording this ? If you did then this oddly sounds as if you forgot to engage it when transferring to digital. The sax sounds exactly like some of my instruments I've recorded with dbx and the played it back without dbx (for experiment sake). The grounding / amp noise, I believe, was recorded on the original tape but now all you're hearing is it going up and down, along with the sax. If you played back the tape with dbx engaged you'd consistently hear the sax WITH the amp / grounding noise, constantly. It's pumping & breathing caused by not decoding the dbx process. Shoot me if I'm wrong.

[Tim Gillett]

I havent heard the clip because of all those registration hassles they seemed to require but actually dbx can sometimes cause that sort of breathing when it IS decoded. It wont breathe like that if you dont decode it. Rather you'll hear lotsa noise in between the sax solo, not so much with it.


You said it is a low Hz sound. I remember a particular model Yamaha 4 track I serviced had worse than acceptable mains hum which would pump up whenever there was program. Unlike many other models, it had a built-in mains transformer, not an external one and the transformer was quite close to the cassette's head. So the hum was not on the tape at all but caused by the transformer.
I thought at the time it was a bad design feature especially since the pumping hum was the reason the customer brought the unit to me. Without doing special mods to the Yamaha there was nothing I could do.

Is yours by any chance a Yamaha with an inbuilt transformer? ie: you can plug it straight into the mains?
Whatever, check by playing a totally blank tape with no dbx or other NR engaged and see how much hum there is. There probably should be more hiss than hum and it should be roughly comparable to the sound of a good ordinary cassette deck.

Also, silly question, if it has an external power pack, is it far enough away from the machine to not induce hum?

Another possibility, an earth or grounding loop picked up by the tape head preamp when the machine is connected to your PC or whatever, could have a similar effect.

The dbx decoder might hold the noise down until program appears and then ramp it all up. It's an annoying effect. A constant low level hum is in some ways more bearable.

HTH

Cheers, Tim.

[A Reel Person]

It's the exact sound I'd consider to be poor dbx performance aka "breathing", (an acute case). I believe it to be a severe dbx decoding problem between your deck and your archive tapes. I rest my case.

PS: there seemed to be an unhealthy dose of flutter in there too, eh?

[MCI2424]

Originally Posted by A Reel Person

It's the exact sound I'd consider to be poor dbx performance aka "breathing", (an acute case). I believe it to be a severe dbx decoding problem between your deck and your archive tapes. I rest my case.

PS: there seemed to be an unhealthy dose of flutter in there too, eh?

Having at last heard the sound, I completely agree. Listen to this guy.

[Tim Gillett]

I cant seem to play the track. "Error on page" comes up. What do I have to do?

Cheers Tim

[rayc]

Tim,
I just checked it & it was fine for me. No need to register etc. It runs with a pop up steam player.