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Dane
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Joined: Mon Mar 14, 2016 11:46 am

Stereo to Mono switch with phase inverter Circuit.

Post: # 43511Unread post Dane
Wed Aug 10, 2016 4:22 am

Hi Everyone,

I am building a switch box to set my audio input levels from stereo to mono.
I know that for the best result a true mono mix of the audio should be made, but then still one of the stereo recording inputs should be phase inverted, something this switch also should do.

Can I get some feedback/check on this circuit?

Please note that I am only familliar with electronics to a very small degree, and only understand some basic principles.
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Soulbear
Posts: 525
Joined: Tue Nov 04, 2014 11:56 am

Re: Stereo to Mono switch with phase inverter Circuit.

Post: # 43526Unread post Soulbear
Thu Aug 11, 2016 5:04 am

Hi Dane,
Looking over your Circuit, if I'm reading it correctly, it looks like in Switch Position 1 the Stereo Signal passes through unaltered. In Switch Position 2, the Signal is Summed to Mono in a similar way to the Circuits within this PDF, but with the addition, that Left Output is in Anti-phase or Opposite Polarity to the Right Output. Just out of curiosity, might I ask what is the reasoning for this Polarity change?
Regards :wink: :P :D Soulbear
Stereo to Mono Summing.pdf
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Stevie342000
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Joined: Mon Dec 21, 2009 2:12 pm

Re: Stereo to Mono switch with phase inverter Circuit.

Post: # 43527Unread post Stevie342000
Thu Aug 11, 2016 6:31 am

Soulbear wrote:Hi Dane,
Looking over your Circuit, if I'm reading it correctly, it looks like in Switch Position 1 the Stereo Signal passes through unaltered. In Switch Position 2, the Signal is Summed to Mono in a similar way to the Circuits within this PDF, but with the addition, that Left Output is in Anti-phase or Opposite Polarity to the Right Output. Just out of curiosity, might I ask what is the reasoning for this Polarity change?
Regards :wink: :P :D Soulbear
Stereo to Mono Summing.pdf
There may be a further issue that needs research not sure it applies to all signals or just to tape but if you are summing tracks to mono you end up with a 2-3dB lift at around 700Hz and this may be where the phase error comes in and thus why the anti-phase is useful. This may have only applied to 3-track tape as stereo was intended to be L-C-R. It was usual to record left & right as normal from microphones and a single microphone was used for the centre track. Thus you got a 3 channel stereo mix, mono mix and a stereo mix. It was usual to blend a bit of the centre track in to the final mix to fill out the whole in the middle. Take a look at Mercury Living Presence recordings, RCA Living Stereo, Decca UK etc, mostly all 3 track recordings from 1954 onwards, they knew stereo was coming so the major labels had a backlog of stereo tapes in the archive ready for when stereo entered the mass market.

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