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Test Tone

Probably a naive question, but having worked with nothing but digital and not having too many years of experience at that, i'm wondering- what is the function of a test tone? What is it used for and why?


RussoR Sun, 03/28/2004 - 10:06

Test Tone at 400Hz +/- 7.5%......???????

Hey all. I'm studying music tech. at uni and I've been given the task to write up a report about some new product I'm supposed to test for a made up company. The problem arises when they ask me to include a "switcheable internally generated sinewave test tone at 400Hz +/- 7.5%" in the system. The product comprises two turntables, a mic, IEC equalisation for the three, a mixer and tone control.

What's already been said in this thread has helped me understand the idea behind the use of a test tone but I'm still baffled as to why they would ask me for it to be at 400Hz specifically... Is this an industry standard? Something to do with psychoacoustics??

I'm really at a loss here and would appreciate any help from what sounds like and experienced crowd. Thanks

(The Bob Vogt website WAS a great read!)

Pango2000 Wed, 03/17/2004 - 14:55

I often use test tones, probably because I work for music AND television.
For broadcast I need test tones so I use them in my studio doing music productions, for level setting and for troubleshooting.

Caine Dreiling Thu, 03/25/2004 - 10:00

I would absolutely LOVE to work in a studio that ran a couple of big gaudy studer 2" or the like. I love to think of the days cruise talks of. Great takes.. magical moments. I was watching the VH1 special on Fleetwood Mac, and Lindsey was cutting and splicing. Those engineers, or anyone for that matter, who masters thier trade inspire me so greatly. We have lost so many of the 'True Masters' in any profession. Most people are just too lazy these days! Sometimes even me.

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AudioGaff Wed, 03/03/2004 - 17:50

In the most basic application, it is used for trouble shooting such as in connection problems. Play a test tone at a specific freq. and go through your signal path to check, hunt down and resolve connection problems and/or to easily be sure siginal is getting from one route path to another.

The more common use was in analog recorders. Analog recorders will drift in speed and levels over time or due to wear but also due to temp and/or humidity. You would use a very special calibration tape with test tones as a reference to align and cal your recorder. In the recording process before any music is recorded you would record several reference test tones on the tape from your recorder so that when it is played back on either your recorder or some other recorder, you would check the tones and make adjustments as necessary to make your deck match the tape before you began. If you didn't do this, instruments on the tape would be out of tune to live instruments, as well as the tempo of the song being different. In digital this isn't really necessary for for the same reasons, but is always a good practice to do and to have so you can check things like reference levels as well as to check on what the proper sampling freq. was used.

Luke Walchuk Wed, 03/03/2004 - 18:53

Thanks a lot! That makes a ton of sense and is crystal clear to me now.

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cruisemates Sat, 03/06/2004 - 02:00

OK... Gaff, I have to laugh because you are usually so much more knowledgable than I am, but analog was my domain. Test tones had little to do with pitch or speed of a recorder.

The idea was to make sure your tape was giving you the frequency response on playback it had on input. For example, you would record a 100 Hz tone, a 1 kHz tone, a 10 kHz tone and a 15 kHz tone all at 0dB on your tape, and then play it back and see if they all played back at 0 dB on every track. If not you could adjust it. In addition, there was a setting called bias which had to do with how hard various frequencies hit the tape as opposed to others.

Tape calibration was fine art, where we would A/B input vs output and get them to match as much as humanly possible for frequency response, and I worked with some of the best engineers in the world.

I often wonder how well so much of our current stuff would stand up to the kind of scrutiny we used to give our analog recordings, because frequency response was a big part of the job of an engineer that seems to rarely get mentioned these days.

Concerning pitch though, one advantage we had was the ability to vari-speed a recording and lower it to record a vocal part a singer couldn't normally hit (I actually used to record the Chipmunks for the NBC cartoon show in the 80s).

I would record an A-440 tone on the tape and then slow it down a specific amount (say 2 whole tones) which I could find by using a tuner and "tuning" the speed of the playback tone to an "F".

I miss tape - there were so many tricks and advantages to having a physical medium to work with: Backwards guitar solos for example. I know you can do that now, but it was more fun our way.

I was one of the best razor-blade editors you ever saw. I could edit classical music and 2-inch masters. I used to "punch-in" entire bands if when recording their bed tracks they had an excellent take that otherwise broke down later on.. and then splice the two pieces of 2-inch together (as long as the tempo matched it worked great).

Todays music has lost so much "feel" because of all the automation and software editing. We have gained tracks and editability but lost the magic of a great take where a group of people get a groove going and do a great performance.

Back in those days I used to dream of what I would do if I had the abilities we have today, but I now realize technology has become more of an influence (and too often a crutch) rather than an asset. Too bad.

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AudioGaff Sat, 03/06/2004 - 09:23

OK... Gaff, I have to laugh because you are usually so much more knowledgable than I am, but analog was my domain. Test tones had little to do with pitch or speed of a recorder.

Well, you may indeed know more than I. I am still very versed in the analog domain with many hours of cal experience. My answer was meant more as a general overview and not a detailed document on the subject. I was only making two points, 1)Analog recorders drift and need periodic calibration in both speed and levels. 2)A test tone cal tape such as the MRL, was one of the tools used to do that. Sorry for any confusion and for not being absoutely accurate...

realdynamix Sat, 03/06/2004 - 10:10

:) I have seen recordings with stated frequency test tones at the lead that were off in frequency when played on another machine somewhere else.

For example, if the capstan motor, servo drive and belt was replaced on the source machine, but the servo was not adjusted using an alignment tape and strobe, or alignment tape and frequency counter. The other machine could correct this with vari-speed and frequency counter, a strobe won't help on the second machine, except to confirm it's own accuracy.

That would be an oversight on the maintenance of the first machine, but most studio techs would/should have their machines default speed(s) well adjusted, and checked often. In house, slight speed variance would not be too big of a problem, but when it travels; things will be off pitch.


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cruisemates Mon, 03/08/2004 - 13:03

Generally - I can say I almost never found drifting pitch to be an issue, tape drives were remarkably stable pitch-wise, and in refernce to using tones to calibrate for pitch the only artist or engineer I ever heard refer to it was Frank Zappa which is where I got the idea for printing an A440 tone on my tapes for reference. Otherwise tones were kept purely for frequency response (freak) and bias calibrations.

Do a Google for a website by a Bob Vogt who worked at A&M studios. Great reading! He mentions a visit from one of Pink Floyd's engineer's as being a "real engineer" who did things like make tape dubs backwards for smoother transients. His experiences were all similar to mine (I also worked in Hollywood in the 70s) We did all that stuff at Producer's Workshop (where we were using Bob Ezrin's 24-trk recorder) and also did something called "rock's biasing" by ear where we fed the machine a sub-sonic tone and calibrated the bias by listening for minimum gravel.

Hey - it's all a moot point now. I wonder of anyone even uses tones for anything anymore. But since we had them in the sturdio I often used them for other things (setting gain on pots for echo returns, etc).

Anyone out there still usng tones for anything anymore?

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AudioGaff Mon, 03/08/2004 - 16:27

In an ideal enviornment where temp and humidity, are well controlled and routine scheduled maintenance is done, there are far less problems and need to cal. I didn't really have this so my experience with speed/pitch drift was more of an issue with both an 24-Otari and 24-Studer. At least three times a year I would need to adjust. Winter cold months, later winter/spring rainy months, and in the hot summer months. It was never off by more than several cents, but seeing as I was already checking freq and levels anyway, it is awlays worth takiing a little extra time checking and adjusting speed/pitch. It would be foolish to not do so.

I still use tones for signal troubleshooting and for levels check. They still have value in checking levels from one systen to another or for one piece of gear to another.

jeeper Sun, 03/14/2004 - 15:42

Strange what test tone can find sometimes. I do not expect it much in audio with exception of word clock because its not common to use a BNC connector in audio. Some 30 odd years ago I did a tour as a communications tech for an independent telco and we frequently checked and tweaked levels through with test tone. Several times I found good looking BNC conectors to yeild 18 DB loss. I do not know if thats an indication of folks word clock problems or not because I've never tried to go digital to digital with word clock here but I've been questioning it in my mind.