Tone generator question

[miroslav]

Go for the Velleman. The TAG 101 is second hand and therefore you cannot trust the calibration.
The Velleman will deliver up to 8volts pk to pk that's about +8dBu and should be plenty. It has a source Z of 50Ohms and so should be fine.

Now! What I need is a pink noise generator of about the same price!

Dave.

That's why I recommended the NTI Minirator earlier.....you get the variety of tones, levels, pink noise and some other functions, all in one box.
For setting up my tape decks or just running audio tests/checks on my gear....the Minirator is a breeze since it's intended for audio/studio use, so all the options/functions are specific. I have the original one...the newer version has even more options.
A bit pricey, but worth it.

 

[ecc83]

Oh man! That`s just great! Thanks for all the help!! I`ll try to get this week and I`ll let you know!

BTW why do you need a pink noise generator? Have seen this Velleman kit?

Cheers

I need a second source of PN to drive guitar amps on destruction tests (well, in fact they hardly ever do!) .
One lot are running on 120V 60Hz generated by a HUGE mother of an amp fed from a precision 60Hz oscillator and the second batch will be fed from raw mains, variac'ed but 50Hz and I want the signal sources to be totally independent.

Thanks for the Vell' link I shall see if the technical director thinks it good enough.

Dave.

 

[Hammerstone]

Clear as mud?

Dave.

Just about. If I'm hearing you correctly, it's important that you disregard the input levels of the tape deck, right? Now is this only necessary when biasing/calibrating? Because I get the feeling that what we're talking about so far is only applied to setting up a tape deck. What about when you just want reference tones at the beginning of your tape, is it any different?

All my multitracks have been recorded on a deck that doesn't sound bad, but is still pretty far from being correctly aligned. I'm really glad I haven't had it properly biased/calibrated yet because those tapes would probably be unplayable then...need to have a final mixdown to 1/4" tape first...

 

[miroslav]

Just about. If I'm hearing you correctly, it's important that you disregard the input levels of the tape deck, right?

How do you mean?

Your test signal source needs to be the correct level for the tape deck's input level.

 

[technoplayer]

I know Behringer gear is generally disdained, but I have one of their cable testers and it has a tone generator with level switching built in
Might not this work??


Behringer: CABLE TESTER CT100

 

[jpmorris]

I know Behringer gear is generally disdained, but I have one of their cable testers and it has a tone generator with level switching built in
Might not this work??

No. I tried that to avoid having to pay for the Minirator. After getting nonsense results, I checked the waveform - it generates a rather rough square-wave, much like the BEEP command on the ZX Spectrum/Timex back in the 1980s and probably in exactly the same way, using the CPU to switch the level high and low at the desired frequency.

It works for a presence check but for any kind of calibration it is utterly useless.
(However, it does make a very nice cable tester)

 

[Hammerstone]

How do you mean?

Your test signal source needs to be the correct level for the tape deck's input level.

Is there a thread for this already? I might have missed it, and I'd hate to have you explain something if you can just send me a handy link telling me exactly how to record test tones for a tape that I'm about to use.

But here's what I think I understand then: to record test tones onto a fresh tape, you need to have a dedicated tone generator send a signal at a specific level, say 0dB, and then the input levels on your tape deck should be where the VUs are reading 0dB also. Right so far?

Now here's what I've done in the past: I went to this site and downloaded a bunch of different tones...I'm reasonably sure I specified 0dB on the level (it's nice that they offer you options). And that's what I used on my tape deck; imported the tones into itunes and put them each in different playlists on infinite repeat, plugged the speaker line out into a mixer, then used main and aux outs to go into all four inputs of my tape deck. And I set the input levels on my tape deck so that all four channels read 0dB at 1kHz (and the rest of the tones are all over the place on the meters...it's pretty far out of alignment).

So I guess my real question is: Is this wrong?

 

[ecc83]

Good morning Hammerstone,

Your very first task is to get hold of a service manual for your tape deck or at least the basic specification.
Next you need a test tape and this really should be a full track recorded commercial jobbie. These tend to be pricey so if you can't afford one maybe someone local can make you at least a 1kHz reference tape and possibly a 10kHz or white noise azimuth tape?

The level ref tape will give a specific output voltage (in dBu as a rule) from the playback amplifiers, usually with external level pots at max. Now check azimuth then go back and re-check level!

Now load up virgin tape of your choice and inject 1kHz (or whatever the manual says) into line input, external line pots at max, AT THE SPECIFIED VOLTAGE LEVEL. Note, it should be obvious I hope by now that you must have some means of measuring audio signals to a fair degree of accuracy and over the audio spectrum. This applies to both the signal out of the machine AND the signals you put in.

Note too that you cannot rely on built in meters because...
1) You have not calibrated them yet!
2) Some meters read the levels POST recording EQ.
3) Even quite expensive VU meters are just a rough arsed signal indicator the dB markings cannot be trusted.

The signals you downloaded or the ones obtainable from Audacity etc are referenced to 0dBFS! The voltage out of the playback device depends upon THAT device.

Lining up even a simple stereo tape machine is a pretty tedious and long winded process WITH the right kit. Without it you are doomed....And we haven't even MENTIONED biasing yet!

Dave.

 

[Hammerstone]

Thanks for the clarification. I guess I have a lot lot more work ahead of me...

 

[duduac]

I have already accepted that I`ll have to buy the Velleman, however, yesterday I had this stupid thought that I wish to share with you guys.

If the tone generator from a good quality software generates a good and stable tone that is coming out from an unbalanced output, can I plug this unbalanced output to a high quality DI box that gives me an balanced +4dbm output and use it as a reliable tone generator ?

It may be a silly idea, but at least I found it creative of my brain to think this way

 

[ecc83]

I have already accepted that I`ll have to buy the Velleman, however, yesterday I had this stupid thought that I wish to share with you guys.

If the tone generator from a good quality software generates a good and stable tone that is coming out from an unbalanced output, can I plug this unbalanced output to a high quality DI box that gives me an balanced +4dbm output and use it as a reliable tone generator ?

It may be a silly idea, but at least I found it creative of my brain to think this way

In theory yes, But you would have to find a DI box with some gain, remember my laptop could not quite produce +4dBu?
Then, even if you had such a box with "unity" gain and you fed it +4dBu the output, if "properly" balanced, i.e. two amps in anti-phase, would deliver +10dBu (I shall let you think about that one!) .

Bottom line: You need to MEASURE the voltages.

Dave.

 

[CSP]

If I read you correctly then ECC83 was correct in saying that the first thing you require is a professionally produced alignment test tape (full track) and with this you get the various heads, etc set correctly --- if the heads are not correct then anything you record on the recorder will probably sound OK when played back on that tape recorder ONLY, played anywhere else and you could/will be in all sorts of trouble (phasing, frequency response, etc ).

For your interest, in a PROFESSIONAL studio, the alignment of the recorders was/is done before every session and if there is a lot of winding of the tape (ie fast forward/rewind), the tape recorders could quite possibly have the test tape process re-done every few hours. Just to ensure that nothing had changed.

After the heads are correct then really any sine wave generator that is capable of outputing the required level, as stipulated by the recorder's manufacturer, will do. You could even use the tone generator on a program such as Audacity (as detailed earlier in the thread).

Remember that if feeding out of a standard PC/Mac, then the output level is most probably -10db or -20db and if your recorder is expecting +4db then you will always be recording that 14 - 24db below the expected level. You would then require some form of Line Amplifier to raise the signal that 14 or 24 db to get the recorder's +4db expected level.

David