Operating level and tape characteristics

[jviss]

(fourth(?) in a series of stupid newbie questions that are specific to Analog - tape, etc.).

So, having my deck back from service for a couple of weeks, I tried something out.

It's supposedly set up for a 185 nW/m operating level.

I recorded a 440 Hz tone at 0 Vu. On new Quantegy 406 it reads back right at 0 Vu. On some old, unknown tape, it reads back 3 dB lower.

Can one infer something about the tape coercivity, or the actual amplifier operating level based on this data?

In addition, the results were off on channel 4. It reads back about 1.5 dB higher than recorded. I tried this both by recording on track four and reading it back, and also by reading back what was recorded by the channel 1 recording amp by flipping the tape over.

(I could have some of this slightly wrong, I didn't take careful notes, which I will do in a future session).

 

[ofajen]

It's supposedly set up for a 185 nW/m operating level.

I recorded a 440 Hz tone at 0 Vu. On new Quantegy 406 it reads back right at 0 Vu. On some old, unknown tape, it reads back 3 dB lower.

So the bias was set for 406? All bets are off on an old, unknown tape. The bias setting is probably not optimized for the unknown tape and that can cause output to be all over the place.

Just for fun, test the unknown tape by inputting a 0VU tone, push record and monitor off playback and then sweep your oscillator slowly across the whole audio band from 20 to 20K and see what you find. A high end that tilts up indicates underbias, while a high end that tilts down indicates overbias.

Cheers,

Otto

 

[evm1024]

Also test this at 1 kHz rather than 440 Hz. The reason is that the EQ reference point is at 1 kHz. Using 440 Hz puts you into the EQ curves which may react differently on a different tape (Not that I wold expect 3 dB difference - I'm grasping at straws here).

-Ethan

PS the sweep should be interesting

 

[jviss]

Also test this at 1 kHz rather than 440 Hz. The reason is that the EQ reference point is at 1 kHz. Using 440 Hz puts you into the EQ curves which may react differently on a different tape (Not that I wold expect 3 dB difference - I'm grasping at straws here).

-Ethan

PS the sweep should be interesting

A sweep might be difficult - I'm using Audacity on a Macbook to generate the tones. I did try 1kHz as well as 5 kHz and even higher. From 440 to 1 kHz it was dead flat, i.e., no change in results at 440 or 1k.

 

[evm1024]

A sweep might be difficult - I'm using Audacity on a Macbook to generate the tones. I did try 1kHz as well as 5 kHz and even higher. From 440 to 1 kHz it was dead flat, i.e., no change in results at 440 or 1k.

I did not really expect a change.... But worth testing.

Do a google search fot software audio sweep generator for a list of free choices.

I use truerta (which comes with a 48 kHz scope in the free version) but the free version does not have sweep. It does have a signal generator.

--Ethan

 

[jviss]

I did not really expect a change.... But worth testing.

Do a google search fot software audio sweep generator for a list of free choices.

I use truerta (which comes with a 48 kHz scope in the free version) but the free version does not have sweep. It does have a signal generator.

--Ethan

Whoops, looks like trurta is windows only; I'll try windows on vm ware fusion later