Improving quality of Poor Tape to CD Conversion

[ptorpey]

I have a CD which was burned from recording from a cassette deck and I would like to improve the quality of this CD version (since the original tape is no longer available).

My guess is that the tape was originally recorded using a tape deck with Dolby. However, the person who converted the tape to CD did not use a Dolby tape deck. Thus, the tape is very hissy and has an excess amount of high-end to it.

I am looking for suggestions on which combinations of processing / effects / filters and their settings which might be elpful in improving the quality of the sound.

Thanks for any suggestions.

-- Pete

[kozikowski]

<<<the tape is very hissy and has an excess amount of high-end to it.>>>

Oh, it's worse than that. Dolby is dynamic. The high end boosting changes with loudness of the show.

You might be able to produce a much better show by simply lowering the harshness overall and call it good.

Edit > Select All > Effect > Equalization. The blue line is a rubber band and you can push it up to get more gain or down to get less. You can put as many points in the curve as you think you need.

I would probably start around 5500 to 6000 and drop as you go up. Tune by listening.

This is a picture of the panel where I changed the "loudness" of a clip.

http://kozco.com/tech/audacity/voiceEq.jpg

Koz

[ptorpey]

<<<the tape is very hissy and has an excess amount of high-end to it.>>>

Oh, it's worse than that. Dolby is dynamic. The high end boosting changes with loudness of the show.

You might be able to produce a much better show by simply lowering the harshness overall and call it good.

Edit > Select All > Effect > Equalization. The blue line is a rubber band and you can push it up to get more gain or down to get less. You can put as many points in the curve as you think you need.

I would probably start around 5500 to 6000 and drop as you go up. Tune by listening.

This is a picture of the panel where I changed the "loudness" of a clip.

http://kozco.com/tech/audacity/voiceEq.jpg

Koz

I was hoping that there was a plug-in or filter which automatically did or undid Dolby effects which might be available. I'm blind and navigate this from the keyboard, so looking at graphs could be a bit tricky (well, impossible!). I guess there are edit boxes for ranges of frequencies that I can play around with. Not knowing the Dolby standard, however, I don't have an idea of what percentages to cut at what frequencies.

Hmmm.

Well, thanks .. I'll try some v alues and see what I can do.

[steve]

There are several versions of Dolby, and some mess around with the dynamics more than others. The chances are in favor of Dolby B, which is not too bad in this respect.

The approach that I would take, is to use the Noise Removal effect to take out most of the hiss, then use the graphic equalizer to reduce the treble if it still sounded too bright.

[Tiger-Heli]

I was hoping someone might have an update to this.

I can't get to the kozco.com pages (problem on my end, not his), but ...

It seems like if it is just a EQ filter setting, someone could post the settings that work, and it could be provided separately or bundled as a "pseudo Dolby B decompression" filter.

I recently transferred a Dolby B cassette using a very cheap tape deck and got outstanding results with Audacity, but I thought the files are still a bit too bright.

I don't have exact numbers with me, but I set the EQ to flat and then dropped down -2 dB at 6000 up to about -6.5 dB at 20000.

I'm thinking of just running the same EQ settings one or two more times, but if anyone has any settings that they were happy with for a one-time pass, I would appreciate it if they could post them.

I realize it will never be perfect, but for these projects, what I have is really good enough, but I'd like to try for a little bit better.

Thanks in advance!!!

[steve]

The exact settings are going to depend on many factors. Cassette tapes tend to become more dull sounding with age (they loose high frequencies and replace it with hiss). Very few cassette players will record frequencies above about 15kHz so you can just roll off above 15kHz to reduce high frequency noise. Between 1kHz and 15kHz is a matter of experimentation. (It would be oh so very useful to have real time Eq in Audacity so that we could adjust while playing, but we haven't).

[Tiger-Heli]

Thanks Stevethefiddle!!!

What I might try and what might get close to the real time EQ is to play the files back in WMP or some other player with a flat EQ setting, adjust the curve there, and then transfer those settings to the Audacity project file.

Unfortunately, in my naivety with this, I saved the raw recording as a project file, and then saved the recording with labels, EQ, noise removal, and click removal, so I no longer have a "base" project to work from, unless I want to redo all of that post-processing (which I don't).

[steve]

What I might try and what might get close to the real time EQ is to play the files back in WMP or some other player with a flat EQ setting, adjust the curve there, and then transfer those settings to the Audacity project file.

Nice bit of lateral thinking

[Tiger-Heli]

Nice bit of lateral thinking

I had to look that up in Wikipedia, but I think that was a complement - if so, Thanks!!!

(If not, I'm okay with that too!!!)

[kozikowski]

Lost in all this is that Dolby® is a licensed process. So somebody would have to write a pseudo-Dolby decoder and then make it public like lame for MP3.

Ray Dolby made his fortune by being one of the people who could do noise reduction on audio tape and few if any people could hear it working. There were others, DBX comes to mind. Dolby cemented his place in time and space by licensing his work to whoever would write a check. The company provided quality control and certification, so you could buy Dolby Noise Reduction® on your $48 tape recorder and some FM radio stations broadcast in Dolby®

Dolby was the first to do commercially available audio noise reduction which in one sweep made large multi-track audio recorders possible. He theorized correctly that you only hear noise when there's no music there. He added distortion so that quiet sounds were made very much louder and loud sounds were pretty much left alone. When you recorded this package and played it back accurately (hence the Dolby reference tones) the quiet parts of the show were restored to their original volume and the tape noise would be reduced by the amount of the original boost.

That was Dolby A. B and C were cassette tape versions without the calibration tones where the high frequencies were also boosted. I went to a demonstration of Dolby C where a live brass quartet played in front of an audience (us). The presenter interrupted the performance claiming he "made a mistake" with his machines and they would have to start over. They did and half way through the second pass they put down their instruments. We were listening to a Dolby tape playback of the first performance, all but indistinguishable from the actual players.

So without the reverse compression, the best you can do is "force" a noise reduction and try to get rid of the high frequency boost. The performance is still going to sound compressed and flat compared to the original show. If you're googling, Dolby was a very special compander--compressor/expander.

Koz