I didn't see an answer to this question.

Summing simply means that a stereo signal has been converted to mono by 
combining the L & R channels into a single monaural channel.

Like when you could throw the switch on your receiver or amp from stereo 
to mono. You are summing the 2 channels. Receivers don't have such 
things anymore.

joe salerno

On 4/24/2012 7:08 AM, James Roth wrote:
> Greetings,
> Would someone please tell me what "summing" is.
> Thanks.
> Ben Roth
> -----Original Message-----
> From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Art Shifrin
> Sent: Monday, April 23, 2012 12:08 PM
> To: [log in to unmask]
> Subject: [ARSCLIST] differentiating groove walls' noises
> It's worthwhile to check if one of the two outputs of a monaural goove is, for a given side consistently inferior or superior.  I just did another early 78.3 (rounded off)  lateral cut lacquer (1934) for Niel Shell (Nat Shilkret was one of his Grandfathers).  The two sides were, thankfully not
> gouged by prior playings with steel needles.   But it had been played
> multiple times on those heavily tracking early systems.  One of the outputs was dramatically less noisy than the other.
> For vertical cut grooves, a method that occasionally (but not consistently) is beneficial is to also digitize both outputs.  Keeping the eq. flat, then apply your best available de-clicker to the two channel digital file.  THEN sum them (with one channel 180 out).  When summing, interactively set the two levels for a maximum lateral noise null. Whether done with early stage declicking or not, always check audibly and or visually.  You'll often find that the two levels are NOT @ unity.  Assuming that your preamp&  cartridge combo is properly set up, then when the level 'discrepancy' occurs, that indicates that the cutter was not functioning on a precisely vertical plane.  For lateral grooves, with the critical difference being that the two outputs are nominally in phase,  the comparable nulling is done to suppress the vertical component.
> For grooves that are intentionally neither vertical nor lateral (i.e. Arto 78s...with their audacious knock off of Victor's "batwing' label), it's anything goes for selecting&  possibly mixing outputs for the best possible results.
> AFTER the nulling is performed and two channels mixed together,  then apply  eq. et. al.
> Best,
> Art (Shiffy) Shifrin

Joe Salerno