Digital Sound on Super 8, Is It possible ?

[Steve Lee]

I must start by saying this is not about recording a soundtrack onto super 8 from a digital source such as a DVD / blu ray, but recording a digitally encoded soundtrack that could be played back in 5:1.

I recently pick up a Philips DCC recorder/player which was developed back in the 90s to rival Sony's DAT recorder.
This machine can play back standard analog compact cassettes, and output the source as analog via RCA sockets or as a digital output through optical. This option makes cassette tapes sound like you have never heard them before.
The main purpose of the deck is to be able to record and playback digital on newly designed cassette tapes. I beleave the reason was so nobody could playback a digitally encoded tape on a standard cassette deck.
After having this unit apart to see what is going on inside, it seems that it records the digital tracks exactly the same way as analog on the same linear moving tape. As there is no difference between the cassette tape and the magnetic track on film, in theory this could be done?
As encoded digital tracks are recorded and stored in blocks that are transferred to a memory buffer before being played back, this would mean that the sound track would have to be recorded double the amount of frames ahead of an analog track on the film. This is so it is possible to read it and then decode it, being digital this means it could have a delay so it is possible to sync the sound with the picture, in the same way that Dolby digital worked on 35mm.

There would be no need for any alterations on the projector, as you are just using the playback head to read the information. Yes a decoder box would be needed that could output the signal back to analog that could be plugged back into the projectors amp.
By doing this it would elevate any pop and crackles, dropouts and tape hiss from the soundtrack, and also could be possible to playback multitrack 5:1 all from super 8.

I would be interested on your thoughts, before I rip the unit apart to see if it is possible to be done by experimenting with it.

[Osi Osgood]

It was always possible with optical sound super 8, as optical sound was printed onto the actual film stock, just like it would be for any 35mm print today, but to my best knowledge, no one ever attempted to with super 8. Besides, it would have required a brand new generation of projectors capable of reading the digital track on the film and reproducing it for our delight, but make no mistake, that optical track was capable of that.

[Joerg Polzfusz]

Hi!

IMHO the combination of small soundstripe area plus slow speed makes S8 „not suited“ for recording digital sound. The best you could probably do is recording image numbers (something like timecode or dts-signals) and then sync it with an external player.
(The above applies to both mag. and opt. soundtracks.)

BTW: you don’t have to rip anything apart - you can simply feed the recorded digital beeps into a computer - like the compact cassettes used as „datasettes“ in 8bit times or fax-signals or 56k-modem-Signals transmitted via ordinary analog telephone lines. When the computer buffers the data, then it doesn’t matter whether the sound-data matches images that are currently shown or that will be shown 1 minute later.

[Joerg Polzfusz]

Your recorded digital data would probably sound like this when not fed into a computer, but directly to a speaker:
https://freesound.org/people/theTone/sounds/209687/

[Peter Watkinson]

Hello,
Great idea but I am afraid that the principle of the Philips DCC machine is far more complicated than you suppose, the tape head is in actual fact nine heads stacked on top of one another, eight for signal digital data tracks and one for syncronisation and housekeeping, the tracks are very narrow less than 0.02 mm wide so the tracking is to say the least critical and the data is written in a continuous stream sequentially sweeping its way down the eight tracks as the last track is being read the 1st track is lined up ready to start the sequence again, this is to artificially increase the tape speed to get sufficient data rate without resorting to an impractically high linear tape speed or a rotary scan. If you have one still working you are lucky the heasd are very delicate and seem to fail at the age the machines now are. I remember it was a even more a technical wonder than the Sony when it came out, but compared to the proven rotary head machines it must have been on the very edge for the manifacturing techniques at the time.

I am sorry to complicate your ambitious project.

[Osi Osgood]

Jeorg, just curious as to why the speed of super 8 sound film is too slow, ad it's as fast as 35mm, 24 fps, or are you speakers ng of a different "form" of speed?

[Steve Lee]

Thank you gentlemen for your input.

First Joerg, this was my idea if it was possible to record a digital pulse tone onto the track, and then playback and decode it would it playback as an audio track. Being from the generation that had to load computer games via a cassette tape and then using a dial up modem, that this track would sound like a modem if played back as a audio track. It was just a thought if this could work using a digital to analog converter.

Peter, thank you, this was the information I was looking for. I couldn't work out how Philips were able to store this amount of information on a linear moving tape without using a rotary scan head. It now makes total sense.
Inside the unit the head assembly has a cover plate on it, so just by looking at it without removing the cover you would never know it has so many connections leading to it.

Osi, when it come to anything analog recorded on magnetic, speed is everything. This will effect the sound to noise ratio greatly. The faster the tape is pulled over the head, the more information is stored onto the the tape as audio.
Super 8 running at 24fps measures 10.1448 cm/sec, compare this to a studio master tape which run at ether at 15ips or 30ips. The slower the tape passes the head it will pick up more of the actual tape rather than the audio recorded on it, and that is were you get tape hiss from.
That is why when 6 track magnetic was used on 70mm, this produced the finest analog sound of all time, it was down to the amount of film in length per second being pull over the heads, that produced the highest sound to noise ratio on any format.

I am going to go down the road of DTS with this, and try to record a time code onto the track to see if it will at least start a disc playing. Maybe it is possible to store the soundtrack on a SD card, rather than a disc.

[Ed Gordon]

Steve, what is your ultimate goal? Are you trying to use a Dolby/DTS sound track with a super 8 projector?

[Steve Lee]

Hi Ed, my ultimate goal is to find a way of ether storing a digital soundtrack directly onto the film, or placing a timecode preferably on the balance track to sync to an external drive, in the same way as DTS work on 35mm.
But most of all to keep it as simple as possible, so you haven't got cables and boxes connected all over the place.
The plan is to have a little box that is connected to the line out of the projector, this box would also contain a SD card reader, and would output via a stereo RCA sockets and a 5:1 optical.


All of the parts and pieces are available to do this, it is just finding away to put them altogether in one unit. Apart from inserting the SD card with the soundtrack on and starting the show it would be totally user friendly.
I just want to see if it is possible to do this, as it has been bugging me for some time now. At the end of the day it is no different to what was developed back in the 90s for 35mm, its just doing it on a smaller scale.

[Ed Gordon]

Do you use mkvextract to get the soundtrack?

So you are looking to replace this player?

[Steve Lee]

The answer to your questions Ed, is yes and yes.
We now have access to software at home, that can allow us to extract multi track soundtracks from movies on discs or downloads, that wasn't available twenty odd years ago.
It is now possible to edit them to our requirements, so them can match the soundtrack of a digest reel. And then by adding a timecode they should in theory stay in perfect sync.
By using a SD card to store the data rather than a DTS style disc, it would make the whole thing so much simpler and easy to use. This also reduces the scale of the unit to something that can fit in the palm of your hand, or maybe attach to the back of a projector.

[Ed Gordon]

The answer to your questions Ed, is yes and yes.
We now have access to software at home, that can allow us to extract multi track soundtracks from movies on discs or downloads, that wasn't available twenty odd years ago.
It is now possible to edit them to our requirements, so them can match the soundtrack of a digest reel. And then by adding a timecode they should in theory stay in perfect sync.
By using a SD card to store the data rather than a DTS style disc, it would make the whole thing so much simpler and easy to use. This also reduces the scale of the unit to something that can fit in the palm of your hand, or maybe attach to the back of a projector.

The introduction of the Matroska format has certainly given us a lot of benefits. I have used it to extract 5.1 audio from DVD's and insert that audio into low budget Blurays that only had 2 channel audio. The ability to insert/remove sections of video without having to re-encode is a real time saver.

I have not had to deal with syncing issue since I have been replacing whole audio tracks in videos that were not edited. My knowledge of how external audio works with 35mm projectors is limited. I assume that the time code is sent from the projector to the disc player which then adjusts it's speed to match where the projector is. If you port this system to an SD card how will the sync work?

[Osi Osgood]

This is all way above my head, but honestly, it's fascinating! I wish you the best in this endeavor!

[Ed Gordon]

Sound and Film have always been a problem

[Nantawat Kittiwarakul]

Considering the relatively low freq response & S/N ratio of Super8 sound (even magnetic ones), I suspect that placing actual digital audio stream to the film itself would be at the very edge of practicality. Minus the error correction / some redundancy there wouldn't be much left for the actual audio data itself - 12-15 kbps maybe.

The more practical solution would be DTS approach. Having timecode on balance track to sync with external player, plus normal audio on the main track as a backup (and for backward compatibility with usual sound projector).

So yes in theory, but who's gonna actually try it out?