Lets colabAnalog Tape Processing: Done cheap at home, but need pro confirmation

[dean1964]

A shift in phase (assuming it's really bad) would definitely screw with tracks that where recorded as a group. Overdubs not so much.

At that point, drums would probably suffer most since the entire image depends on the tracks being in phase.

Me testing for that would actually help me decide if it's worth processing group tracks for, or just saying "don't run group tracks through tape, just tracks that are not phase dependent to other tracks."

Vocals would be a good one, assuming they are tracked in mono.

Actually, anything that is panned dead center, rather anything that is not panned full to one channel or the other, would be effected by the phase shift. The left and right channels would be shifted relative to each other, so every relationship a between a particular instrument and more than one speaker will be colored by the shift. Processing individual tracks this becomes a non-issue.

Honestly, I don't agonize this much over phase when I am working. However, it is very important to be aware of it, and check a correlation meter from time to time.

 

[LeeRosario]

Honestly, I don't agonize this much over phase when I am working. However, it is very important to be aware of it, and check a correlation meter from time to time.

I agree, as long as it sounds good and it's not changed too much

 

[SouthSIDE Glen]

The AGC thing really does through a wrench into my thoughts...only cause I wonder if it's really an AGC circuit that's affecting my signal and not the actual tape response itself.

Even if there's not a true AGC like Tim reports, you still have the question of gain structure to wonder about, especially since you mention you don't know really how hard you hit the tape.

The audio tracks on VHS HiFi are similar to an FM radio signal; the resulting amplitude of the record/playback signal is determined not by the strength/amplitude of the magnetic signal on tape, like on standard open-reel and cassette decks, but rather the signal level is translated into a frequency modulation of a carrier frequency. This not only greatly reduces tape hiss, but it fairly negates the whole idea of using analog tape saturation as a dialable effect. Now perhaps there may be some "smearing" - for lack of a better term - of the modualtion that might possibly impart some small effect on the playback (I don't know, that's just off-the-top specualtion), but it wouldn't be of the same nature at all of whet we're used to with standard amplitude recording.

What this means is that the relative "amplitude" of the playback signal is ultimately limited by the bandwidth of the frequency modulation. If/when the modulation tries to exceed the top end of it's usable bandwidth, I believe it will result effectively in clipping on playback, because the modulation frequency will simply top out.

The question is how that machine is calibrated in that regard. Does the bandwith top out at 0VU (-10dBV) like Tim suggests? If so, it's rather like digital in that there is zero headroom above the "zero" signal. While I don't factually know one way or the other, that sounds rather restrictive to me; I'd tend to (read : I WANT to ) believe that there is at least a few dB of headroom above -10dBV before the FM signal maxes out.

The kicker here, Lee, is that it's awfully difficult to spot clipping with a square wave .

I'd send a sine in, and pay attention to the signal level being sent to the deck, trying a signal (minimally) at -10dBV(-7.8dBu, consumer line level) and -4dBV(-1.8dBu, 6dB over consumer line level) and compare results. Any further testing would be based upon the results of that test, I should think.

G.

 

[LeeRosario]

Even if there's not a true AGC like Tim reports, you still have the question of gain structure to wonder about, especially since you mention you don't know really how hard you hit the tape.

The audio tracks on VHS HiFi are similar to an FM radio signal; the resulting amplitude of the record/playback signal is determined not by the strength/amplitude of the magnetic signal on tape, like on standard open-reel and cassette decks, but rather the signal level is translated into a frequency modulation of a carrier frequency. This not only greatly reduces tape hiss, but it fairly negates the whole idea of using analog tape saturation as a dialable effect. Now perhaps there may be some "smearing" - for lack of a better term - of the modualtion that might possibly impart some small effect on the playback (I don't know, that's just off-the-top specualtion), but it wouldn't be of the same nature at all of whet we're used to with standard amplitude recording.

What this means is that the relative "amplitude" of the playback signal is ultimately limited by the bandwidth of the frequency modulation. If/when the modulation tries to exceed the top end of it's usable bandwidth, I believe it will result effectively in clipping on playback, because the modulation frequency will simply top out.

The question is how that machine is calibrated in that regard. Does the bandwith top out at 0VU (-10dBV) like Tim suggests? If so, it's rather like digital in that there is zero headroom above the "zero" signal. While I don't factually know one way or the other, that sounds rather restrictive to me; I'd tend to (read : I WANT to ) believe that there is at least a few dB of headroom above -10dBV before the FM signal maxes out.

The kicker here, Lee, is that it's awfully difficult to spot clipping with a square wave .

I'd send a sine in, and pay attention to the signal level being sent to the deck, trying a signal (minimally) at -10dBV(-7.8dBu, consumer line level) and -4dBV(-1.8dBu, 6dB over consumer line level) and compare results. Any further testing would be based upon the results of that test, I should think.

G.

Good kick in this one. Alot of good sense all up and down this thread.

Honestly, I was looking into trying this approach on a current album I'm working on, but like Rich Costey says, any responsible engineer takes an oath not to kill the patient.

I definitely don't wanna kill the good textures I'm getting before the VHS thing.

In the mean time, I'll definitely be obsessing with the tests, including the sine wave test. I'm thinking of going as far as trying to find an affordable used Professional grade VHS machine.

I mean they're pretty much extinct now, so they can't be THAT expensive, right?

 

[SouthSIDE Glen]

I mean they're pretty much extinct now, so they can't be THAT expensive, right?

Well, that NEC I linked to in the earlier post was a grand total of about $35 with shipping included. Can't get much cheaper than that .

But I'd be very wary about buying that stuff unseen and untested and without known provenance. We're talking machines here that are a good 25 years old, have had God knows how many public rental tapes of rust run through them, and who knows how many hours of motor and head wear. Then there's the criticality of tracking alignment with that helical scan format. I know you know about all this from old Studer maintenance, but it can be even more of a problem with an old VHS machine because they have usually suffered more use, misuse and abuse than your average 2' studio machine has, and to a mechanism of decidedly less engineering quality.

Then again for $15 hardware and $20 shipping, it's not a very expensive gamble . But without a proper working quality and maintained machine (or refurbishing, if needed), obviously your test results on such a deck would be pretty meaningless.

I still have my old NEC down in the basement, which is where all my old electronics end up. But it doesn't work. If you need it for parts, we can work something cheap out .

G.

 

[StevenT]

I must be strange

I came up with a strange way of getting my digital recordings to sound softer like tape.

Although I do have few nice VST's dedicted to exactly that (tape emulation), I do it manually sometimes.

My digital recorder has 8 outputs (one for each individual track).
It's a Korg D888 recorder.

When I want the warmth, I record on digital, play it back to a multi-track tape recorder (Fostex 8-track), rewind the tape.
Create a new set of virtual tracks on the Korg Digital, and play the 8-tracks of tape back in to the Korg (as individual tracks), and record from the fostex.
No Sync problems, tape warmth (and track bleeds), it's all there.

Then I take the korg tracks (records each track as a seperate .wav) and I bring in to DAW (Magix Sequoia) for final mix/mastering.

I designed my studio on purpose to be able to do digital recorder, analag recorder, or daw very much on purpose.

I find advantages to each of them depending on the project I am doing.
When I want to do retro, aint nothing like tape... IMHO anyways!

 

[pat regan]

This is my very first post to this forum,thank you. I record myself on a multitrack editor (vegas) the usual way by building up track upon track using various intruments. I use one or two inputs for each overdub. To get analog tape sound, I run the live input to a tape recorder (Otari) that allows monitoring the playback head as it records. The output from the tape recorder's playback head goes to the digital converter. I adjust for the delay between record and playback heads (about 78ms. on my machine) by time shifting the overdub in the editing software. Every 20 minutes or so I rewind the tape and reuse it over and over. I get the ease-of-use of digital multi-track recording with the richness of tape pre-lay. Think of the tape recorder as the perfect tape emulator except that it produces an unintended delay which must be corrected after each overdub. I'm giving away one of my best techniques here in exchange for all the great ideas I've gotten from this forum.

 

[leddy]

I'd be reluctant to send audio through an old VCR. Audio fidelity was not a priority for those things I imagine. Maybe I'm wrong...

But,

If you want tape - you can get a decent reel to reel deck for peanuts nowadays. I have a couple of Tascam 22's. Both less than $100. I have a 22-4 four-track I paid less than $200 for. They all function great, tape is still readily available, etc.

They sound great, and they have meters so you know how hard you are hitting the tape. I've done tests like running a 1khz sine wave through at different levels and measured the harmonic distortion. Fun to mess with. I also like to mix in to it and record the output from the play head back into the PC on the same pass so there is no audible wow/flutter. Removing those artifacts makes an old Tascam sound as stable and solid as any pro tape machine.

I still prefer tracking to tape and mixing to digital, but that's not always possible. Tracking digital then mixing to tape and back makes for extra D/A and A/D. Tracking to tape first is only one trip through the A/D upon mixdown.