Cassette to (Dolby) Digital

Audacity Help Forum Windows
1

Hi,

I’m new to posting here, but have lurked for a little while. I decided to dive in and post up my question.

I’m using 2.0.5.

I have recently undertaken a quite large project of digitizing a collection of cassette tapes. All are live (vocal) recordings, some are over 40 years old. Most are first generation copies of the masters. Some are extremely high quality recordings, some are crap that sound like they were recorded through a pipe, and everywhere in between. I have no illusions as to the abilities of Audacity, as it seems many that post questions regarding sound enhancement, etc, often do. Garbage in, garbage out.

That being said, I am curious as to how, for the really good recordings, I might be able to export them as Dolby Digital. Now I know that tracks that were not recorded in Dolby format are hard to mix down into it, but I’m willing to try, and am willing to accept that they won’t be “true” Dolby Digital. I have found very few post regarding this, most have danced around exporting to DVD audio, if I read them correctly. I have so far been unable to find a concise answer, so I decided to ask.

I would ultimately want to play the cleaned up recordings on a surround sound system.

I am using a laptop and a Sony boom box to digitize to stereo. I have, so far, been pleased with this setup, and have had no issues that I am yet aware of.

Again, this is a long-term project, and I am in no hurry to do this tomorrow, but want to start thinking about the process, possibly buying other hardware, etc.

Cheers!

2

Dolby Digital is heavily patented and actively protected, as is just about anything “Dolby”, so as you say, you are not going to get “true Dolby” without using real Dolby products.

Also, you can’t make “true surround sound” from mono or stereo.

What you can do, is to “clean up” the recordings using various tools such as noise reduction, equalization, hum filters and so on to get a mono or stereo recording (the sound quality will still depend on the quality of the original), and/or you can fake a surround sound effect.

Precise details depend a lot on the equipment that you are using and the kind of effect that you are after, but here are a few ideas that you can experiment with:

To fake surround sound, the basic idea is that you create suitable tracks for each of the output channels, then export a multi-channel file in a format that can be played on your equipment.

To export a multi-channel file from multiple tracks, see here: http://manual.audacityteam.org/o/man/advanced_mixing_options.html
Note that the correct channel order depends on the format, and some players do not use the “correct” channel order, so you may need to experiment.

Widening the stereo separation of front left and front right can be done using this Channel Mixer plug-in: http://wiki.audacityteam.org/wiki/Nyquist_Effect_Plug-ins#Channel_Mixer
Instructions for installing the plug-in are here: http://wiki.audacityteam.org/wiki/Download_Nyquist_Plug-ins#Installing_Plug-ins

To create a “centre channel”, use “Tracks > Stereo Track to Mono”

To create a Low frequency channel (if required), apply the Low Pass Filter effect to a mono mix.
If you have a separate Low frequency channel then you may want to reduce the low frequency content of the other channels so as to avoid too much bass.

For rear channels, you may want to add a slight delay to the sound - you can do that by adding a short period of silence to the start of the track. Experimentation will be required for best results, but to avoid it sounding like an echo it will need to be less than 50 milliseconds.

3

Thanks for your reply.

I forgot to add one key question in my initial post: do I need a sound card capable of multi-channel output to export multi-channel audio? I remeber reading that somewhere, but that has been a while back, probably is outdated information.

I did read the link to the manual that you posted above.

I’m sure that I will probably have more questions as I move forward, especially regarding cleaning up these recordings. More on that at a later time.

Thanks again

4

You don’t need any special sound card for exporting an multi-channel file.

In order to play multiple channels you will need hardware that can do that. (Audacity does not support multi-channel playback, though you can play multiple “tracks” through a normal stereo sound card).

5

Actually, you CAN export to “Dolby”. It’s called AC3 and the optional FFmpeg import/export library can do it!

I’ve never used Audacity for this, and I’m not sure about creating a 5.1 Channel AC3 with Audacity. However, I have used a FREE program called [u]wavtoac3encoder[/u] for encoding 5.1 channel & stereo DVD soundtracks. You feed it 6 separate WAV files, and it makes a 5.1 Channel AC3 file.

There are “legal issues” and a royality is supposed to be paid when copies of the encoder are distributed. I assume this is why FFmpeg is not automatically included with the Audacity download or available directly on the Audaciy website. (I know the LAME MP3 encoder is not included with Audacity for that reason.)

You can get a licenced Dolby AC3 encoder if you buy DVD authoring software (Corel Video Studio for example). And, since the only “standard” way to play Dolby Digital is on a DVD or Blu-Ray, you might consider getting DVD authoring software and making a DVD.

The most common way of making an “audio DVD” is to make a “slide show” DVD or a DVD that shows a “still picture” of text with the artist & song title. (There is a special format called DVD-Audio, but it doesn’t support Dolby AC3, most DVD players can’t play it, and it never caught-on.)

The truth is, for music you’ll generally get the best results by keeping the original stereo recording and using one of the Dolby Pro Logic II Soundfields on your home theater receiver to generate surround-sound. I don’t know of any software Pro Logic decoder that can decode stereo into Dolby Digital Surround. Plus, doing it on-the-fly with your receiver (or soundcard) saves you the trouble of encoding and allows you to change the soundfield settings at playback time.


That said, I have “remastered” a mono concert DVD into 5.1 surround using some of the techniques suggested by steve… I created “fake” left, right, and center channels by using sligntly-different and complementary EQ in each channel. Then I panned the sound to the center during talking parts and panned the applause toward the rear. And I took applause from one part of the concert used it for rear-applause during other parts. For the main concert parts, I added delay and reverb to the rear channels. (On this DVD, I also kept the original mono track because I really screwing around with the sound.)


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A note about the “point one” LFE channel… The LFE channel is supposed to be for “low frequency effects” (booms & explosions). The other 5 channels are supposed to contain the regular bass.

If you play a 5.1 channel track on a stereo setup, the LFE is not included in the automatic downmix. (So if you do create a point-one channel, do not remove the bass from the other 5 channels).

However, home theater receivers have “bass management” which optionally routes all of the bass from all 6 channels to the subwoofer. This allows you to use 5 “small” surround speakers that are not good at reproducing bass.

6

Thanks, Doug. You can export up to a 7-channel AC3 file using Audacity with FFmpeg.

The main difference between Audacity and wavtoac3encoder is the encoder used. FFmpeg uses a native (I suppose reverse-engineered) AC3 encoder that FFmpeg regard as giving the highest quality of all the compressed formats that FFmpeg supports ( https://trac.ffmpeg.org/wiki/GuidelinesHighQualityAudio ).

Wavtoac3encoder uses the Aften AC3 encoder ( http://aften.sourceforge.net/ ) which is now a little different to the native FFmpeg AC3 encoder.


Gale