Bias calibration CD by Vince666
I want to share with you something that I found interesting. User ‘Vince666‘ from Tapeheads has built an interesting CD for performing deck calibration. If you have a good 3-head deck and you like to do good recordings, you probably know that adjusting bias for a particular type of tape is a must.
Some advanced and modern decks have an internal system with a special tone generator that allows to do this easily. Other decks have a Bias control but no internal generators.
However, even with modern decks equipped with internal generators, it’s very difficult -if not impossible- to perform a good calibration because of the characteristics of that particular tape.
Here’s the original explanation from Vince:
i don’t know if it does exist some test CD made not for the “multi-purpose” testing of the HiFi systems but “only” to give you the test tones to correctly calibrate the bias/level to record into any cassette tapes…
i think it could be useful for all those people who have (for example) a 3 head deck without any auto-cal feature and/or without the inbuilt tone-generator…
my current deck is a 3 heads Pioneer without auto-cal and without any generators, so i needed some specific CD to do the bias calibration (without the need to connect the deck to the PC for the test tones every time i want to calibrate a new cassette on it).
and so i decided to make myself the tones and the CD.
we all know that the most used tones (to calibrate the bias/level) are 400Hz , 1KHz , 10KHz , 15KHz… but, while doing this specific test CD i thought to add also some other tones (such as 315Hz , 8KHz , 12KHz) , some noises (white and pink) and also some double tones (in stereo) to have 2 tones at a time (one for each channel)… for example 1KHz/10KHz or 400Hz/10KHz into left/right channels (but also many other “coupled” tones)… and i also did the “swapped” stereo ones (for example 10KHz/1KHz for left/right , etc) that could be useful to check for the symmetry between the channels or to “optimize” the tuning even if the deck hasn’t the separate left/right bias knobs…
at the end of the work, my CD contains 24 different tracks made only to calibrate the tapes for recording.
If anyone was interested about this CD then i’ll be really happy to upload it for you all TH members.
at the moment i’m going to sleep (it’s late night here) and, if you like, tomorrow i’ll give you more details and eventually will upload it somewhere on the net for you all. CHEERS
As this post is old, links are all dead, so I uploaded to my dropbox folder with the permission of Vince and here they are:
Later Vince decided to update the CD: “ i will start attaching on the next post some new tones i’ve made this summer and which i find even more useful in some way. “. And here’s the link for this tones:
And here’s the description for the new tones:
1 – Sine 315Hz_2min [-1dBFS]
feed it to the deck’s inputs and tune the input record level in order to read 0dB on your deck’s meters (or any other level you may need).
This is useful to set the tape’s sensitivity (cal. rec level) so that the input signal matches the level of the recorded one.
2 – Sine 315Hz_30sec [-21dBFS]
once you’ve set the input record level with the previous tone at 0dB on your deck’s meter, without touching the input record level knob anymore, you can be quite sure that this tone would be enter the tapedeck’s inputs at -20dB on deck’s meters (which generally aren’t that much precise at these lower levels), since the difference in level between the previous tone and this one is just 20dB.
3 – Sine 10Khz_30sec [-21dBFS]
you can evaluate/set the bias calibration (with the common “two tones” method) just by recording the previous 315Hz and this 10Khz tones, which are both at the same lower level, while trying to get a tape recording where these tones are re-played from the tape at a similar/equal level… this should give you a reasonably flat frequency response while recording on most tapes.
4 – Sine 20-20K_30s [-21dBFS]
again, it’s useful not to touch the input record level set with the first track at 0dB so that also this fourth track will be feeded at the deck’s inputs at -20dB.
This is a sort of replacement of a common “continuous” sweep tone from 20Hz to 20Khz…
The main difference is that here you don’t have a continuous sweep tone varying from 20Hz to 20Khz but i’ve created a bunch of small segments, each one at one fixed frequency… The main advantage in using this method is that it’s way easier to read the recorded results (i.e. if you capture them from tape to your PC’s soundcard) since you can easily know which is the frequency of a certain segment since they are easy to locate even by eyes.
The whole tone-sequence from 20Hz to 20Khz is long only 30 seconds and i’ve managed to put some very short tones between any of them as a sort of markers which help you distinguish the things both visually and/or by ear.
But i think it’s easier to directly show you a map of this tone sequence with a picture (which has the same file name as the audiofile)…
Look at the picture…
There are 30 “measuring” tones at different frequencies (from 20Hz to 20Khz) which are long about 800 milliseconds each one and all at the -21dB digital level on CD.
Between any two of these short segments, i’ve put a very short (around 150 milliseconds long) tone at 315Hz at the same -21dB digital level (highlighted on the picture with those orange vertical lines).
But, i’ve also thought to mark the things even better by putting a very short (around 200 milliseconds long) tone at 400Hz at -18dB digital level each 5 frequency tones (highlighted with the green vertical lines on the picture)…
Then, resuming… you will start hearing a very short “marker” tone at 400Hz at the beginning (and these 400Hz tones are 3dB louder than the rest of the tones and “markers”)… then you will hear a short 20Hz tone, then a very short “marker” tone at 315Hz, then a short tone at 40Hz, then another very short marker tone at 315Hz, then a short tone at 80Hz, then another very short marker tone at 315Hz, then a short tone at 130Hz, then another very short marker tone at 315Hz, then a short tone at 250Hz, then a very short marker tone at 400Hz and which (again) is 3dB louder than the rest… and so on until the end of the track…
The point to add the 400Hz markers each 5 tones and at 3dB louder level was to easily see (and hear) that you’ve just passed 5 “measuring” tones (the louder markers have a different “sound”, being at a different frequency than the other markers, and also have a taller waveform being slightly louder than the rest)… this way you will easily know which is the frequency of the “measuring” tone you’re focusing your attention on.
I know it seems difficult to explain… but if you simply listen to the track while looking at the picture then everything will appear extremely easy to understand (and to use).
I hope you’ll find these tones as useful as i do,
Thanks to Vince666!