I suspect that you are left with your 'next step.' Without a sync pulse
of some kind you are essentially 'spitting in the wind.' Verifying your
turntable speed is an obvious thing to do. Using a clock on your A/D
converter may help. However, some A/D converters have worse specs when
used with a clock & some clocks are very poor (you get what you pay for).
Make some tests using a short file. 15 or 30 seconds should be enough to
see things like drift, etc.
Beyond the obvious, I'm at a loss for suggestions. Keep us posted.
Corey Bailey Audio Engineering
On 12/19/2020 9:20 PM, Tim Gillett wrote:
> Hi all,
> I've familiar with the principle of summing two audio recordings of
> the same programme where the wanted programmes are time coherent but
> the unwanted background noises arent, making it possible in theory to
> realize a 3db reduction of the background noise. I've used it on
> cassette and 1/4 track "stereo" recordings which are actually dual
> mono, although time alignment can be a little tricky and an "azimuth"
> tool can really help.
> Earlier 78 RPM recordings are understandably noisy especially as I
> believe was customary, the original metal parts were usually recycled
> for cost reasons so all transfer engineers have to work with may be
> the best shellac consumer pressings that have survived.
> The other day while browsing I chanced upon a seemingly mint
> condition 10" 78 shellac record of Eileen Joyce performing
> "Berceuse" in 1939. Here's a modern CD release of it.
> Quite noisy and limited bandwidth, even for 1939 I thought. I
> cleaned and transferred the disc I'd found and after declicking
> compared the sound to the version linked to. The two versions sounded
> close. Signal to noise was about the same.
> I believe that compared to vinyl, shellac was a relatively noise
> medium so it occured to me that assuming the stamper had less noise
> than the shellac copies, it should be possible to time align the audio
> from the two discs, sum to mono and yield a potential background
> noise reduction of 3db. Not huge but with an already noisy recording,
> not to be sneezed at!
> So far I've not had much success. I'm having problems trying to
> accurately time align my disc transfer with the commercial release.
> I can get them within maybe a few milliseconds but it's not enough.
> The two versions drift in and out of sync causing comb filtering.
> My next step might be to find another mint disc of the same
> performance and make my own transfer of both on the same gear under
> the same conditions so at least there is a fighting chance of an
> accurate alignment. Maybe a better turntable with more precise speed
> Has anyone tried this technique with 78 RPM shellac records or have
> any comments?
> Cheers Tim.
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