Headphone Optimizer Pro (HOP)

How it works

The HOP is an amplifier developed specifically for headphones. It individually compensates for the manufacturing tolerances and non-linearities of a specific pair of headphones: the headphones were measured precisely, so that headphones and HOP form one sonic unit. The headphones therefore reproduce the recording closer to the original – with recordings in 3D binaural stereo (dummy head) as well as with conventional stereo recordings.

The individual acoustic optimisation is entirely analogue – free of any digital technology in the signal path. A microprocessor handles the operation: volume, balance, crossfeed and basic settings are adjusted with a rotary encoder and stored as user presets.

The sound quality of the Headphone Optimizer Unit (HOU) and the Headphone Optimizer Pro is identical; the two models differ in housing and features:

• HOU: black-and-gold aluminium housing with headphone rest; volume control via a relay-controlled Alps potentiometer
• HOP: aluminium housing in half 19-inch width (1 U), optionally rack-mountable; additionally a crossfeed circuit, a balanced headphone output (4-pin XLR), a mono switch and storable playback settings

Features

• Integrated, individually adjusted optimisation circuit in purely analogue technology
• Integrated class A output stage
• Fine-stepped analogue volume control via relays (100 dB control range), operated by a rotary encoder; channel tracking < ±0.1 dB
• Switchable four-stage crossfeed circuit (push-button) that reduces the exaggerated channel separation of conventional stereo recordings on headphones (menu item C)
• Microprocessor-controlled user interface with storage of several user presets (menu item P)
• Four different basic settings (menu item S)
• Fine left/right balance control (6 dB range) via the built-in rotary encoder (menu item B)
• Switchable diffuse-field equalisation (menu item D)
• Decoding of M/S stereo recordings (push-button) and mono switch (push-button)
• Gold-plated 6.35 mm headphone output (mutable by push-button); input signal switchable to the XLR output (push-button)
• Balanced XLR line inputs and outputs with high-end Lundahl transformers and gold-plated Neutrik connectors
• Gold-plated 4-pin XLR output for headphones with a balanced XLR cable
• Compact, lightweight aluminium housing (approx. 2.2 kg), optionally mountable in a 19-inch rack (1 U)
• On request, the HOP could be recalibrated when the customer changed headphones

Technical data

Feature	Value
Frequency response	20 Hz – 100 kHz
Volume control	relays, 100 dB control range, channel tracking < ±0.1 dB; fine balance control 6 dB
Crossfeed	four stages, switchable
Inputs	balanced, XLR (Lundahl transformers, gold-plated Neutrik connectors)
Outputs	balanced, XLR (Lundahl transformers); 6.35 mm headphone output, gold-plated; 4-pin XLR headphone output, gold-plated
Operation	microprocessor control with rotary encoder and push-buttons; user presets
Housing	aluminium, half 19-inch width, 1 U (rack mounting optional)
Dimensions (W × D × H)	217 × 260 × 44 mm
Weight	approx. 2.2 kg

Individual calibration

As with the HOU, every pair of headphones was measured and linearised individually and channel by channel – entirely analogue, free of any digital technology. Why this is necessary is shown by the frequency response measurements on the page of the Headphone Optimizer Unit.

In use at Cybele Studio and on location

At Cybele Studio the Sennheiser HD800 is individually linearised in the analogue domain by the HOP. Especially on mobile productions in churches, sacristies or smaller chamber music halls, where no ideal loudspeaker monitoring is available, this system provides reliable sonic control from the sound check onwards and throughout the recording.

In post-production the HOP serves the sonic assessment of mixes and masters and the creation of binaural 3D versions – the rendered binaural versions of Dolby Atmos and Auro-3D productions. Spatial positioning, depth staging and tonal balance are controlled through fully linear headphone reproduction.