subject: Sony APR-5003V, notes on bias
updated: 2010-11-24

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ladewd

Posted: Mon Jun 14, 2004 11:54 am    
Post subject: Re: Record bias - how to indicate on a track sheet?

Hey Sissy, 

Good info on the bias. I may be a bit crazy, but isn't the description of too much vs too lilttle bias backward? I find too much bias causes the machine to lose the hi freqs and sound dull, and too little causes the high end to be distorted. I did a lot of studies with overbias when 996 and 499 came out. I had to determine the best distortion vs frequency response for the APR series machines (gap = .250, same as the Studer). I consistently needed more bias than the manufacturer's recommendations to minimize distortion and keep the freq response flat. 

That being said, I prefer the sound of a slightly underbiased machine. Maybe its the fact that I played in too many loud bands as a youngster. When all my friends liked stuff with heavy bass, I always prefered a beefier top end with a tad of distortion. I'm one of those weird people with perfect pitch, but with a catch. I found the high frequencies helped me hear the overtones more clearly, which made it easier to figure out what was being played. As soon as a recording sounded the slightest bit muddy, identifying the notes being played became much more difficult. 

CA

http://messageboard.tapeop.com/viewtopic.php?t=15773\
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ladewd

Posted: Mon Jun 14, 2004 5:31 pm    
Post subject: Re: Record bias - how to indicate on a track sheet?
 
Quote:
Hey, CA, while we're on the topic, I've always wanted to use a distortion meter to check my bias. Any suggestions? I can't buy one of those fancy $20K units that you lug around, but I'm interested to do a little measuring. 

BTW, the APR series is the most underrated machine in the history of audio. Damn they're good! 

S-H, 

You won't like what I'm going to tell you. I use an Audio Precision. I don't know what the going rate is for used units these days, but I sold a System One for about $1500 last year. There is also a box by Sound Technology, which is even more ideal for this purpose. It allows you to measure just 3rd harmonic distortion, which is what you're really after. I don't remember the model number but it is described as tape recorder analyzer (1500B seems to stick in my mind). It does things like Freq response, and flutter as well. Its about 15 year old technology, so you should be able to get one fairly cheap if you can find one. It'll interface with a computer and give you printouts as well. We used to use them at Sony on the APR QA line to spec out machines. I'm sure there are cheaper solutions. We used to use some distortion meter at MCI, but I can't remember what the hell it was called. I just found this and this on ebay. They're not exactly what I was talking about, but they are distortion analyzers and nice and cheap. 

Speaking of APR's. You are correct. IMHO, I think they're very underrated. I just sold my APR-16 last week. I feel like I lost my best friend, but in the process I bought some UAD-1 cards for my mac and a new sound card for my PC. I just don't have the room for that stuff here at home, or the budget to buy tape. I strickly run a one-man-show at home and my computers have become my best friend. I still have my APR-5003V though and will never give that up. I even found a nice stash of headstacks for it. 

About the bias, yes you are correct, but I was talking about 1/2 db either way and not a gross mis-alignment. 

Later, CA
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Jim Williams

5/10/2005

Most recommended bias setting supplied by tape makers are all wrong. Not only that, they will vary for each channel and will change over time with head wear. There is only one precise way to determine obtimum bias levels. Use a distortion analyzer. 

I use an Audio Precision to do this. I set up a rapid distortion vs freqency sweep from 50 to 10k hz. It draws over about a 5 second period, then blanks and redraws. Once playback alignment is set, feed the 10k hz tone and adjust the bias for lowest THD. You would see that the distortion curve is like a smile. Add more bias and the low end THD goes up while the high end THD goes down. It's like rocking the smile back and forth. I set it for lowest THD at about 1k. You will still see 4~5% THD in the lows and in the tops, thats just tape nonlinearity. I have set record levels on JH-24's and JH-110C's to +9 with the 911/996 tape. I managed to lower THD from .55% at 250 nw to .15% at +9 relative to 250 nw. Just learn not to slam the meters. That's 2/3 less dirt with 6 db better S/N. In the 'ol days that's when the Dolby SR's were shut off.

Jim Williams
Audio Upgrades

http://www.gearslutz.com/board/high-end/33032-bias-basf-911-a.html
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Jim Williams

5/10/2005

If your analog machine has .1% W+F, you better check the motors. Most "pro" analog machines offer .05% W+F. You can also replace the bearings with type 9 aerospace grade. This will lower W+F even more. I did this to an MCI JH-24 about 20 years ago and it lowered W+F in half. It was so stable even 10k tones were solid. It almost looked like a Studer A800!

Since you are measuring distortion from .1 to 4%, .05% W+F won't matter. Besides, you can see the flutter drawing on the analyzer as well as the thd levels moving with frequency. If you are concered, just run the W+F test on the Audio Precision to check if it's OK. If you want a tighter bass, adjust the distortion "smile" to lower in the bass. If you want cleaner tops, adjust the bias so the smile lowers at the top end. I prefer the smile to be even from top to bottom.

Once this is done, a chart can be made to stick on the side of the machine. Other engineers will appreciate this effort. Then go ahead and repeat for a different brand of tape. Now you can put it to rest for 6 months. After that, do it all again to compensate for head wear.

The 10 hz bias noise trick is very good once you know what to listen for, but won't show the variations in frequency vs distortion like the analyzer. The AP method is simply more precise.

Jim Williams
Audio Upgrades

http://www.gearslutz.com/board/high-end/33032-bias-basf-911-a.html
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Jim Williams

5/2/2007

The only proper way to determine ideal bias is to use a good distortion analyzer like Audio Precision. All the recommend bias levels provided with the tape are WRONG!

They will also vary between each track. It will also vary with wear. I use a THD vs. frequency plot which re-draws every 5 seconds. This way one can "see" the effects of bias on THD. I send enough to lower THD to around .15% at 1k, much better than the provided spec of .55%. Then you can tweak the HF record EQ to flatten it out as you can see the curve as you do it.

Any other way is a complete guess.

Jim Williams
Audio Upgrades
http://www.gearslutz.com/board/geekslutz-forum/122285-bias-tricks.html
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Jim Williams

5/2/2007

Increase the bias, it brings down hf response and distortion, a good thing. Most recorders have enough hf record EQ to find the sweet spot. I used to get those MCI machines down from .55% at +3 levels to .15% at +9 levels with 996 tape.

Jim Williams
Audio Upgrades
http://www.gearslutz.com/board/geekslutz-forum/122285-bias-tricks.html
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Jim Williams

6/26/2009

Doesn't have to be if you see what's happening on the analyzer. Dolby HX was developed to overcome the increased bias effects of hitting tape harder with lot's of high frequency content, it added energy to the bias waveform and increased bias and lowered hf response.

.2% is not typical. I measure .5% typical on a stock recorder at 250 nw at 1k hz. The THD curve is not linear, it appears as a smiley face, with lowest THD at 1k with 100 hz and 5k hz passing 4% THD. One can optimize THD vs frequency with bias. You can lower it in the bass at the expense of the tops. Or do the opposite.
I like to get it pretty even. 

A modified record/play tape machine can do much better. I have reached .15% at 1k hz at +9 db (520 nw) on an MCI JH-110C. That's far better than the stock measurements of .55% at +3 (250 nw).

As to frequency response accuracy, just pin pointing 1k and 10 k leaves the rest to chance. That's were the frequency response sweeps on the AP help out. You can see the bumps and maybe smooth them out a bit IF you can see what you're doing. Otherwise, it's a crap shoot. Yes, many hits were done with crap shoots, still, it doesn't make it right.

Then you can use the AP for other set ups like tension and wow and flutter measurements. You can use it to phase align the stereo heads. You can use it to calibrate the recorder's meters.

That is if those things are important to you. I've never tested an analog recorder that didn't have some or most perameters set incorrectly. Even a new machine needs a complete going over after transport.

Jim Williams
Audio Upgrades

http://www.gearslutz.com/board/so-much-gear-so-little-time/361322-studer-a80mkii-calibration-repro-eq.html
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