Signal merge

Dear Team ,

I am trying to understand the Signal Merge functionality in Sigma Studio Toolbox .

When I merge a stereo signal say L and R content and feed it to the Signal Merger how is the resultant signal different from its original counterpart in terms of

1.Amplitude

2.Phase

3.Frequency .

Important:

Long story short what is the characteristic of the output  signal that is merged from it's left and right channel and how is that useful ?

  • 0
    •  Super User 
    on May 6, 2021 1:13 AM

         Hello,

         Really there's nothing special about the Signal Merger.  It's exactly the same as the Signal Add block with one additional feature:  Besides adding the inputs, it attenuates according to the number of inputs.  Its wiki entry is rather disappointing since it doesn't even say how much it attenuates.

         When you add signals together, the result may or may not be louder than just one signal.  If adding identical in-phase signals, their amplitudes add directly.  Two identical signals add to double (+ 6 dB), three add to triple (+ 9.5 dB), etc.  The Signal Merger is designed to attenuate according to how many input pins it's been grown to.  A two-input merger has a gain of 1/2 (-6 dB), a three-input merger, 1/3 (-9.5 dB), a four-input merger, 1/4 (-12 dB), and so on.  The idea is to eliminate the possibility of excessive output level causing clipping downstream.  Again, a Signal Add block does exactly the same except without the attenuation.

         The case of non-identical signals adding together is more complex.  Two persons singing a duet won't necessarily sound louder than one person singing.  Adding together the L and R channels of a stereo source is the usual way to produce a mono signal.  Phasing between the two channels may cause some parts of the original stereo sound to become louder than other parts -- mix down a stereo recording of Peter, Paul, and Mary, and in the worst case, you may wonder where Paul went.  Generally, though, it's not such an extreme problem.  Adding signals is also, of course, what a microphone mixer does.

         Thus your questions about amplitude, frequency, and phase are not about the Signal Merge block itself but rather, about adding signals generally:

    •      The output includes the frequency components from all the input signals.
    •      For unrelated signals, their average total RMS amplitude is the square root of the sum of the squares of the inputs
                  (where the amplitudes are expressed in linear values, not dB values).
    •      The phase is difficult to define except for some special cases

    One special case is two sine waves of the same frequency, each with their own amplitude and phase.  Their mixed output amplitude and phase can be calculated using a kind of math known as phasor arithmeticThis Wikipedia article describes phasor arithmetic. It even gives the formulas by which you can calculate the output amplitude and phase for those two same-frequency sine waves added together.

         Best regards,

         Bob