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Topic: Some questions related to tapes (cassettes) (Read 3521 times) previous topic - next topic
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Some questions related to tapes (cassettes)

Hey guys, I have a few questions regarding audio cassettes:
  • Do you know where I could buy some metal (Type IV) cassettes in Germany? The (online) shops I checked only offer normal (Type I) and chrome-dioxide (Type II) tapes.
  • Is the bias for Type II and Type IV different? If not, what happens if one's recorder only differentiates between Type I and Type II?
  • I have a cassette that was recorded with Dolby B, but the player (a walkman) I use for recording to MP3 does not "support" any Dolby number. How can I apply a de-emphasis afterwards using Audacity?

Some questions related to tapes (cassettes)

Reply #1 –
I don't recall for sure, but I think the bias is different. The result of not using the correct bias is reduced high frequency response. If you are using a walkman player that is like any that I ever heard of, you don't need to worry about that anyway, because there isn't going to be any significant HF out of that device anyway.

It is extremely unlikely that you can restore the dynamic range in software. You must use Dolby playback to get the proper results.

Some questions related to tapes (cassettes)

Reply #2 –
Yes, type IV bias is much higher than type II
Using too low bias current will result in exaggerated high frequency response. This is what you will get using metal tape on your deck...

Dolby B is not just another preemphasis, it is a dynamics compressor for high frequencies (> 5 kHz??)
It should be easy to simulate this with software, but I don't know of any that does 

Some questions related to tapes (cassettes)

Reply #3 –
Dolby compression is both frequency and level dependent from what I've read. There have been many discussions of it around the web. Its nature apparently makes it extremely difficult to simulate in software. There may well be patent issues too.

Some questions related to tapes (cassettes)

Reply #4 –
Quote from: Sebastian Mares on
  • Is the bias for Type II and Type IV different? If not, what happens if one's recorder only differentiates between Type I and Type II?

The bias is only relevant during recording. For playback both Type II and IV use the same (70 µs) eq.
Metal tape allowed higher record levels, so you should check if your player can handle them.

It's a pity that there is no Dolby (A/B/C/SR) plugin available. As stated before it's probably a patent issue since it can't be too difficult to implement with modern DSP technology. The Dolby website states: "Today the analog soundtracks on virtually all 35 mm movie release prints are recorded with Dolby SR." Apparently they still sell quite some hardware units so I can imagine that developing a (cheap?) software version wouldn't be high on their priority list.
 

Some questions related to tapes (cassettes)

Reply #5 –
I am usually forced to play without Dolby all the cassettes that I recorded with Dobly B, because the loss of high frequency caused by the tape ageing causes much distrortion when Dolby is applied during playback.