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Old 23rd April 2014, 01:33 AM   #1
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Default summing to mono

I use the HearBack Technologies system in my studio, but a number of folks find it distracting to have some stems in their left ear, others in the right.

The Hearback is a great thing as it lets the musician mix their own darn headphone mix... which changes as the session goes on

the down side of the 8 channels system

Channels 1&2 are a stereo pair (that's life you live with it)
3, 5, & 7 are L

4, 6, & 8 are R

3 can be stereo linked with 4, 5 with 6, etc, but this limits the amount of individual track control as the stem sends need to panned to the middle... otherwise they're still hard-panned L and R

I'm thinking of making a small passive summing "amp" but I'm wondering

a) the headphone signal is too hot and would need higher value resistors

and b) if so, would I need to add a stage of gain to bring the signal back up (which means the circuits now becomes an active circuit and a PS is required)

I've does searching around, but what circuits I've found seem to be directed at summing multiple stereo signals into a single stereo output) I want Stereo -> Mono

I contemplated just making an adapter plug that would short the TRS to TS... but I'm suspect this is a flawed idea...and rather that smoke a piece of gear, thought asking for advice was wiser
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Old 23rd April 2014, 01:54 AM   #2
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Location: San Antonio
Originally Posted by stainlessbrown View Post
I've does searching around, but what circuits I've found seem to be directed at summing multiple stereo signals into a single stereo output) I want Stereo -> Mono
Multiple stereo into single stereo would be, as example, an 8-to-2 mixer. You want a 2-to-1 mixer. The circuits are basically the same, only scaled down. Searching "mixer" and "summing amplifier" in these forums should result with just what you want.
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
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Old 23rd April 2014, 02:00 AM   #3
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Location: Carlisle, England
I ran a mobile disco for many years where the stereo was summed into a mono channel.
No one ever commented on it not being stereo.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 23rd April 2014, 02:47 AM   #4
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Sofaspud- I've tried numerous searches, summing to mono, summing stereo to mono, stereo to mono converter... I'm not finding what I'm looking for

The dilemma is the digital output is sent to the HearBack which has it's own gain stage ( and it can get quite LOUD... some of my cherished old musician friends still needs to go to Spinal Tapped... when 10 isn't quite enough....) Between the digital output and the analog of the Hearback, it's a balancing act to avoid clipping/distortion, hence my concern over adding another stage of gain

The isolated mono in left or right headphone seems to really affect some people more than others, so if I can sum after the Hearback without introducing distortion, the ability to control individual stems remains a plus.

I've contacted Hearback and they will modify the headphones to all mono channels (although they are still 4L and 4 R and the mod involves eliminating the limiter (which is designed to protect your ears form transient spike

I suppose the beat approach is to start breadboarding and do A/B recordings to compare the waveform amplitudes

Rolls had a small headphone distribution amp Rolls DA134 that had a mono/stereo out switch, but I cannot find a schematic for it... I'd like to see if the switch activated a simple passive summing

Last edited by stainlessbrown; 23rd April 2014 at 02:53 AM.
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Old 23rd April 2014, 03:17 AM   #5
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Location: Croatia
use pc based mixer ..but that has some lag that what you doing affecting the material that goes to cds? becouse on some songs i find very different tones on each channel and that makes me nervous i would rather hear only mono
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Old 23rd April 2014, 03:36 AM   #6
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I'm on a Mac Digital Performer-RME FF800, Audient ASP008, Lucid 8824 (mainly used as the clock)

HearBack has no affect on the final mix, it's just for the performer's headphone mix while they are recording. latency is 1.5 msec... and while some say they can hear it...most cannot...and if there is any lag in the recorded track it is compensated for
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Old 24th April 2014, 07:02 PM   #7
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Audio Signal Mixing

Pay particular attention to Figure 4. That's what you need. Separate attenuation for each input included.
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Old 24th April 2014, 07:29 PM   #8
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