Stereo Base Control, A Little Theory; Stereo Base Control, What It Does; Balance; Headphones Outputs / Balanced Connection - Zahl HM1 Manual

Reference headphones mixing amplifier

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Stereo Base control, a little theory

A special feature is the possibility to adjust the stereo width. The perception of spatiality when listening with

headphones differs from listening with loudspeakers. Instead of a cross-feed circuit, we use our stereo base width

setting. It is based on the mid/side technique which is commonly used in professional studios. It provides

additional benefits.

The stereo signal is converted into a mid signal (in simple terms, what L and R have in common) and a side signal

(in simple terms, what distinguishes L and R). Summing mid and side signals in a 1:1 ratio will result in the original

stereo signal. However, if you change the ratio between mid and side before summing them, you change the stereo

base width. In our circuit, we leave the mid signal as it is. We only adjust the level of the side signal. If we lower the

level, the stereo image becomes narrower, if we raise the level, the stereo image becomes wider.

You have direct access to the perception of spatiality. With a music programme which seems too "wide" in the

headphones, one will turn the control one or two steps to the left. If you perceive a recording as too "dry" (centred),

turn the control one or two steps to the right. The leftmost position is mono. This is the preferred setting for early

stereo recordings, when individual instruments have been mixed to the extreme left or right - without spatial

reference.

Professional users check the spatiality of their mix with this function and may discover possible problems,

especially in the extreme positions.

Also important: With the DIR (Direct) button, this stage can be completely switched out of the signal path.

In this way, the purist approach is taken into account.

A precision potentiometer with 21 detents is available for balance control. The centre position is perfectly

calibrated and haptically clearly defined. In fine increments, left/right volume differences of up to about 2.5 dB -

caused by music programme, headphones or individual perception - can be compensated.

XLR 4-pin connector and ¼ inch jack socket are wired in parallel and are intended for alternative use. Theoretically,

you could use both at the same time, the power amplifier is strong enough. However, for a reference quality

listening experience, we do not recommend such use.

Ideally, the XLR 4-pin is used in conjunction with balanced wired headphones. In this case, the signal currents of

the two power amplifiers are not mixed with each other, mutual interference is impossible. The HM1 can unfold its

full quality (also refer to chapter "Dual Mono Design").

DETAILS | P.13

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