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[Bernardo]

Can anyone give me the basics on how to get tracks sounding different according to how much you overbias?

FWIW right now I´m mixing to 1/2 inch 456 tape at 15 ips. I tried overbiasing 3db, I felt the top end got too agressive, almost brittle, so I went back down to 2.5db, which seemed a little veiled, but still better than before. What´s the logic in the process?

Thanks!

[wwittman]

When you say overbias, you mean at 10k right?

the OLD method was to overbias about 1/2 dB at 1 k, but using 10k allows for essentialy biasing based on the heads, rather than just the tape's characteristics.



the general idea is: the more bias current the lower the distortion but also the less highs...
so more overbias yields CLEANER but darker, so you need to turn the hi freq record EQ back up to compromise, and eventually you run out of room to do it.

on the other side, less bias will give you better highs without as much EQ boost BUT more distortion.

if you are biased AND completely aligned at 3 over, then you take the bias back to only 2.5 over, you should immediatley find that the highs in record go UP... it gets brighter.
So I don't understand why you find it sounds "veiled"... you actually should need to take the highs down after decreasing the bias.

unless you meant 3 over at 1 k which is WAY too much bias current and will no doubt sound dull.



3 over at 10k I have to say works well for me on the ATR102 and on most machines


What machine are you using and do you own an actual MRL or other test tape to align playback with?
Are you sure BIAS is your issue?

[Bernardo]

Thanks a lot for the detailed reply, William. I aligned to a fairly new (and original) MRL tape, at +6 (too much, maybe?). I made a mistake on my first post, I meant to type 1/4 inch tape, though, which is what I'm using. And I'm overbiasing at 10k.

When I tested my original alignment (overbias: +3db), I recorded a track from a mastered CD to the two track (a Sony APR5002, btw), and I felt the cymbals, especially the hi hat, came back with extra sizzle, way too much, I felt. Then I redid the whole record alignment for +2.5db overbias, and felt the track sounded more natural, but lacking a bit in top end compared to input. What I ended up doing today is increasing 0.5 db in the HF record alignment, which sounded better to me.

I'm thinking perhaps what happened in my original alignment is that, since I'm working in +6, I was so close to distortion that the top end distorted first (or at least in a way that was easier for me to notice), so that's what I heard. Could that be right?

No, wait, I just read your post again, it's the other way around. I'm a bit confused.

I didn't really think about the fluxivity, perhaps +6 is too much for 456.

I've read about people working the bias on the kick drum track of a multitrack so that it'd sound better.  In that case I'd be using higher overbias for that track, is that right? In your experience is that kind of meddling a good idea?

[Jim Williams]

+6 is too hot for 456 unless you want that Roy Thomas Baker saturated sound.

The APR Sony is a problem as the alignments are made in 1/4 db steps for recall. These are too large and I found the setting to be a compromise due to the 1/4 db stepping.

The cards that the tape makers send off for bias recommendations are wrong. These are starting points. The only way to nail it is with distortion analyzer like the Audio Precision. Run a distortion vs frequency test. I set it from 50 hz to 10k hz with a rapid sweep and re-draw. You will "see" the distortion curve vary with bias. You will also see that more bias lowers THD in the highs, less lowers it in the lows. I go for lowest THD at 1k hz. The THD curve will look like a smiley face, with increased THD at the lows and tops. Typical THD at 10k hz will be around 4~5% THD. The same goes for the low end, 4~5% THD below 100 hz.

With GP-9 tape, levels can be set higher to +9 db, a 6 db increase in S/N ratio. I found with the AP THD tests I could take a MCI JH-24 from .55% THD at +3 levels down to .15% at +9 db levels, quite an improvement and well beyond the manufacturer's specs for the machine. The Sony APR's were always "between" the sweet spot due to the 1/4 db resolution.

[wwittman]

You don't say the level of the MRL tape or what you ref when you say +6 or +3

+ 6 over 185 is the RECOMMENDED flux level for 456.

+ 6 over 250 is the "RTB" (or mine) level and it's in no way "too much" for 456 unless you cream the meters and even then it's not on some things.
Personally I don't pound the meters becasue I like the sound of the tape working not the front end of the tape MACHINE being slammed.


but you also don't say what level the programme went in at.
Modern CD's are cut VERY hot (big news)...

transferrring straight out of a CD player into the 2 track, it's very conceivable that you were hitting +4 VU the whole way...
way too hard to hit a 500 nW/m alignment (assuming you DID mean 6 over 250 and not 6 over 185)

if that's the case, it makes sense that you probably were hearing distortion artifacts maing the HH sound 'spitty' or "too bright"

why backing the bias down would help, I really don't know.
it shouldn't.

what you want in a tape machine is for 0 at 10k going in to come back OUT as 0 at 10k.. right?
also, do you align the low end in playback while recording?
if the low end is too hot at 100Hz, it can make the subjective overall sound "dull" even though the top is 'right'

[drumsound]

Do you go back to the record level and high frequency allignment after setting overbias?  That's what I was always taught to do.  Set input and rec level at 1K set high freq at 10k do overbias then go abck to level at 1K and EQ at 10K.

[Bernardo]

Thanks everyone for the great replies.

By +6 I meant 355 nWb/m, which is the reference level to my MRL, and also where I set my 0 VU.

I redid level and HF record alignment after changing bias. I also did adjust LF repro in record both times.

I also found the resolution of the alignment for the Sony to be a little too coarse.

My meters don´t spend a lot of time over zero, though it's mostly me trying to play safe, not much experience there.

I did go through two tracks of my desk when making the transfer from the CD to the Sony, and I tried not hitting tape very hard.

I'll keep all of your thoughts in mind next time I go into alignment, I'm hoping to get better at this thing. In Brazil it's very rare that recording engineers know how to do their own alignment (can't think of a sigle one right now), I'm trying to be an exception.

[wwittman]

6 over 185 (355 in your case) nW/m is NOT at all hot for 456.

as stated it's the recommended operating level.

sounds like you're doing it right.

are you sure your machine is working correctly?

and do you have a meter for your oscillator so you know you're actually feeding the input of the machine at 0 VU?

[Bernardo]

Actually I don't really know if it is 0 VU, I'm sort of having to roll with it. The machine seems to be fine, but then, I wouldn't know. Sounds good to me.

[scottoliphant]

a 1k tone at 0vu should read around 1.23 volts on a meter. you can check it on each channels output as well to make sure you are getting what goes in (assuming the cards are set for standard operating level and all) and adjust input accordingly. you can then set your vu meter pot to make sure it is reading true 0