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Re: NBSC Player / Recorder

PostPosted: Sun Dec 02, 2018 3:47 am
by Monochrome
Hi Dom, Steve

Dom wrote:
Please post up your isolator, or maybe an article in the newsletter?

I will post the prototype here. Its still a work-in-progress but I will post the results asap.

Steve A wrote:
Sorry, I realise that this is off-topic, but it is worth raising as it does concern everyone's safety.

I dont think safety issues can ever be off-topic and doubtless this issue will crop up from time to time when we interconnect NBTV aparatus and PC's/laptops.



Re: NBSC Player / Recorder

PostPosted: Mon Dec 03, 2018 4:10 am
by Monochrome
Hi Dom (and anyone else following this thread),

A small update on the audio opto-coupling between laptops, so far so good and I have an almost working prototype but have run into a couple of snags.

First of all when trying to play an nbsc wav file from an mp3 player for testing purposes (the nbsc demo with all the idents) I find the audio waveform is inverted from the mp3 player (just pot luck) and nbsc player does not appear to have a button to correct this. Or is it me just not spotting it?

Secondly, does anyone know of a l-o-n-g playing nbtv 32 line standard video file I can download in wav format? I am looking for something that has a fairly constant output and good syncs and plays for at least 5 mins or even longer. This is so I can load it into my mp3 player for testing of the opto coupler. Something like the "SongClip1930.wav" from this forums files area but longer in duration if possible to avoid re-starting the file every few minutes.

BTW the above mentioned wav file passes from the mp3 player via the prototype opto coupler very well when displayed using NBTV The Big Picture V1.2 which has provision for inverting the audio. Of course I could add an inverter stage to the opto coupler but would like to keep it really simple if possible. Currently it uses just one transistor and the opto coupler plus a handfull of support components. I have it running from 5 Volts derived from a 9 Volt battery and a regulator but intend to "steal" the +5V rail from the USB port for the TX side (LED) of the opto-coupler. That of course assumes the 0V rail is common to both the laptops audio I/P (Mic) and the USB port. I hope so otherwise it could get a bit more complicated :-( This supply rail and/or 0V return could also be to noisy to use but we shall see.

I have some more "tweaks" to try over the next week or so (work/family etc permiting) and then I will post again with a schematic of the working prototype. Currently its just a bunch of bits on a bread-board but at least I am not getting "tingles" and "shocks" when I connect the CRO or other bits of gear. I am also looking at a further possible simplification or "misers dream" but thats for the next version.



Re: NBSC Player / Recorder

PostPosted: Mon Dec 03, 2018 4:50 am
by dominicbeesley
Hi Des,

Invert input is an option that I need to add to the player, I keep forgetting. I'll try and remember when I'm back from my travels as it is a common problem. (It's probably worth adding an invert button to your coupler too).

Are you playing raw .wav files or compressing them to mp3 - if you do the latter the colour probably won't work as mp3 tends to mangle high frequencies.

Here's one of my favourite test files ...

PS: You may need to turn "sync tip speed" up to around 66% on the sync settings page, I'm not sure why, it must be something I've done recently

Re: NBSC Player / Recorder

PostPosted: Tue Dec 04, 2018 12:50 am
by Klaas Robers
There is a long comic-film on the MUTR NBTV-CD. If you go to (the website of the NBTVA) you can download the complete contents of the MUTR-CD in zipped .wav format track by track.
- Go to
- Choose for "Hot News". (This is not so hot anymore)
- Look in the second item: The MUTR NBTV compact disc
- in the last line of it there is a link to " be downloaded in .wav format"
- Follow that link and you come on "The MUTR NBTV compact disc" page.
- Follow "Click here" to go to the download page.
- Then "Download" for upright polarity,
- and/or "Download" for inverted polarity.
- Unzip the files.

This is a more than 6 minutes of uninterrepted NBTV video.

If you follow the instructions in the right way, you may make more than 26 minutes or even more of uninterrupted NBTV video. Use Audacity to "glue" the .wav-files to form a much longer .wav file. These files have a well controlled beginning and ending, at the position of a (missing) frame sync.

Re: NBSC Player / Recorder

PostPosted: Tue Dec 04, 2018 3:39 am
by Monochrome
Hi Klaas,

Thankyou for posting such detailed instructions. I downloaded the the files you directed me to and they are exactly what I was looking for, plenty of greys and much more interesting to watch than a test card :-) Having the option to replay both normal and inverted versions of the video files is very usefull when the O/P polarity of the player is unknown.

Use Audacity to "glue" the .wav-files to form a much longer .wav file. These files have a well controlled beginning and ending, at the position of a (missing) frame sync.

Thats a very good idea and would also make a very good demonstration for NBTV. My skills with Audacity are limited but joining audio files together is not to difficult. I have just been playing one of the files and the sync is very stable.

Kind regards,

Des (M0AYF)

Re: NBSC Player / Recorder

PostPosted: Tue Dec 04, 2018 4:04 am
by Monochrome
Hi again Dom,

I am using uncompressed raw "wav" format files with a cheap mp3 player that plays various formats including wav and mp3. A few years ago I also tested various recording and replay methods and found mp3 to be passable though degraded just as you described compared to the uncompressed wav format.

Just out of interest one of the media types I tested was Sony's "Mini Disk" format. It uses an interesting form of compression in which none of the frequency components are lost but to save space it puts gaps or holes in the audio stream. Because the gaps/holes are of short duration the human ear/brain fails to notice but with NBTV recordings the video has a black "blocky" pattern running through it though sync remains fairly stable and fine picture detail remains intact though seriously interrupted.

It's probably worth adding an invert button to your coupler too

I was hoping to avoid that and retain the KISS approach but I know your right and to save time and frustration later on I may as well add a few extra parts and include video polarity switching.

Thankyou for the colour cartoon in NBSC format, it will be interesting to see if replaying from an mp3 player effects the colour or phase in any way. I will follow your advice and try adjusting the sync tip speed as you describe if I encounter stability problems. The use of the mp3 player is only for convenience while testing and I plan to go laptop-to-laptop as soon as the opto-coupler is sufficiently stable in operation or until I get fed-up fiddling with it :-)


Des (M0AYF)

Re: NBSC Player / Recorder

PostPosted: Thu Nov 12, 2020 1:00 am
by dominicbeesley

@lowtone pointed out that my website was broken. I've made a new version, same place, different style!