It was shot on video and then post-dubbed, as the sound recordist messed up. Is there any way of improving the very flat, canned sound?
It looks like a 60Hz+harmonics de-hum notch-filter has been applied,
when it should have been 50Hz+harmonics.
I’ll see if I can find the original audio direct from the tape.
Here’s a sample, direct from the original Betamax capture.
I would just remove the first ~4 harmonics of that 50Hz mains hum
https://plugins.audacityteam.org/nyquist-plugins/effect-plugins/filters-and-eq#hum-remover
even then there’s going to be ringing as a consequence of the notches.
Betamax, before-after
Thanks - I’ve installed the plugin, but I have no idea how to find it or even use it. I must admit I’m a bit of a newbie to Audacity.
Also, is there anything else I can do you make the entire soundtrack sound less artificial and canned?
In Audacity3, (once installed and enabled), its on the old effects list in the “n/a” folder.
After notching out the mains-hum, a bit of treble-boost 5kHz-8kHz
1980 Betamax sound stops at 10kHz: beyond 10kHz is just hiss noise which should be removed with EQ or low-pass filter.
In hum remover I select 50Hz, then there is the option of an odd or even harmonics slider. I also see a threshold level - I’m a bit confused about what does what. I should also mention I have some hearing loss.
It’s possible to see what the dehum filter (rather than hear) is doing on the spectrogram
Thanks so much for your help, I really appreciate it. Here’s a spectogram with the hum removed, as per your suggested settings. The feature is around 83 mins long.
With multiview:
Just need to increase the treble and reduce the hiss now. What filters are best for those?
Above 10kHz only consists of hiss, a steep low-pass filter at 10kHz will remove it
Thanks - what would be best to increase the treble/top end?
Bass and Treble in the realtime effects menu can be adjusted to taste in realtime.
Using a graphic equalizer is more precise, but the native Audacity equalizer is not realtime.
Thanks - here’s a sample clip with all of the above filters applied. Anything else I could possibly do to improve it more?
Less notches:
if you notch out all the mains harmonics it adds an obvious reverb/delay effect which, IMO, is worse than the mains-hum. As I mentioned previously I would only notch the first use 4 -5 harmonics of the hum.
I used the settings you kindly suggested above - I can go back to the original file and re-do the settings, but I’m afraid I’m rather clueless about the settings/filters. Should I go back and change something? 
My suggestion was 2 odd & 3 even …
That’s 5 notches, whereas the Betamax-V1 spectrum has >>50 notches.
Second attempt - with harmonics adjustments as per your post.