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Sonifex Telephone Hybrids Analogue HY-03


Digital DHY-03 Digital Hybrid

The DHY-03 telephone hybrid is an enhanced redesign of the DHY-03 , the best performing telephone hybrid in the world.



Telephone hybrids, or telephone balance units (TBUs) provide the interface between professional audio equipment and the public telephone network. They provide protection for your equipment and the public telephone lines, allowing for varying line signals and line conditions. Automatically cancelling out the unwanted signal they also facilitate two-way communication down a single telephone line.

Sonifex offer a full range of automatic analogue and digital telephone hybrids.

Outstanding Quality From Industry Standard Telephone Hybrids

Telephone hybrids, or telephone balance units (TBUs) provide the interface between professional audio equipment and the public telephone network. They provide protection for your equipment and the public telephone lines, allowing for varying line signals and line conditions. Automatically cancelling out the unwanted signal they also facilitate two-way communication down a single telephone line.

Each telephone hybrid has a telephone line connection, a handset connection and separate terminals for audio input and output from a broadcast mixer, or other professional audio source.

A large proportion of Sonifex hybrids are used in radio and television broadcasting applications for allowing external callers to be connected to the studio mixing console. Most of the other units are supplied to communication operations for allowing extremely effective conversion between 4-wire audio circuits and standard telephone lines.

A ringing detector can be used when you need to answer a call automatically, for instance, if a journalist files a report to a PC recorder over a telephone line, the call can be picked up after a set number of rings by the ringing detector. Both the HY-03 & DHY-03 have a built in ringing detector that is enabled by one of the configuration settings switches on the rear panel.

Analogue, Digital or GSM or HD Voice?

Sonifex offer a few different hybrid units:

  • The HY-03 analogue telephone hybrid.
  • The DHY-03  DSP based telephone hybrid.
  • The DHY-04 DSP based telephone hybrid.
  • The DHY-04G DSP based GSM hybrid.
  • The DHY-04HD DSP based HD Voice & GSM hybrid.


The analogue HY-03 hybrid is suitable for most general telephony applications and is often used in radio and TV stations, trading floors and conferencing centres. The HY-03 can be used for any application where a clean telephone signal is required and the line is not subject to signal delay.

The DHY-03 offers near perfect performance, using DSP power to dramatically improve the unit’s operation. The DHY-03 offers the features of the HY-03, but has some other benefits:

  • Echo cancellation is possible and distortion of other mixed signals is greatly improved.
  • Digital hybrids are more tolerant to fluctuating line conditions and are especially suitable for dealing with calls that have a slight signal delay, for example, satellite and conference calls. The DHY-03 can recall signals from its memory buffer and allow for these delays without impairing performance.


The DHY-04 is a redesign of the DHY-03 hybrid and adds Ethernet connectivity with a built-in web browser for configuration, control and dialing, combined AES/EBU digital and analogue audio inputs and front panel speed-dial buttons.

The DHY-04G uses a GSM SIM card to connect callers on the 2G/GSM cellular network to a radio/TV mixing console connected to the DHY-04G 4 wire input and output.

The DHY-04HD uses a 3G SIM card to connect callers on the 3G cellular networks using HD Voice wideband audio to provide a high quality audio call. This is ideal for broadcasters and journalists providing a frequency response up to 7kHz (twice that of a normal GSM or POTS connection). It converts 3G or GSM calls to the 4 wire audio signal to and from a connected mixing console.

Note: The HY-03, DHY-03 and DHY-04 products are operating on analogue telephone lines, not ISDN or IP digital lines. The “analogue” and “digital” refer to the processing used in the units.

Additional information

Weight 2.2 kg
Dimensions 38 × 30 × 6 cm
Product can be split into multiple boxes




Ship Separately





Key new features of the unit include:

Auto-sensing combined analogue or AES/EBU XLR input.
AES/EBU sample rates up to 24 bit/96kHz accepted.
Configurable analogue or AES/EBU XLR output.
Ethernet port for remote configuration via web browser GUI.
Remote dialling and line hold control via Ethernet.
Ethernet network interface can generate SNMP Traps for SNMP management systems.
DTMF dial tone recognition for reporter remote access – a journalist can dial into the unit which can recognise a pre-programmed DTMF numeric password to automatically connect the journalist on-air.
Four front panel speed-dial buttons for dialling internally preset phone numbers.
Front panel Redial button for redialling the last number.

The DHY-04 also has the following features:

Fully automatic – adapts to varying line conditions and has automatic signal limiting.
Fully adaptive echo cancellation to 127msec – default is 24msec.
70dB typical line balance rejection offering superb performance and crystal clear audio.
Front panel input and output gain controls.
Front panel LED metering of receive and send signals.
Built-in conferencing for 2 hybrids, so that a single telco channel on a mixing desk can receive 2 calls.
Integrated ring detector – automatic call answering after a pre-determined number of rings.
Automatic call disconnection. Fitted with K-break, line polarity reversal and dial tone disconnect detection, defined by the country selection.
Automatic ducking facility allows the talent to ‘shout-down’, or talk over, a caller by reducing the gain of the caller’s signal if it goes above a certain level.
Local and remote line hold switching – calls can be remotely switched through a mixing console.
Line hold/release button to control line hold circuit, illuminates to indicate the status of the line and flashes to show ring status.
DTMF tone recognition allowing a opto-isolated GPI output to be made on receipt of selected DTMF tones, e.g. for starting a studio automation recorder automatically to record a remote telephone interview.
International operation with built-in configurable settings for each country. Country selection allows the unit to provide line impedance and a simulation circuit to match the country.
RS232 serial port for remote control of the TBU & DTMF tone dialling.
Remote port distributes the remote line connect switch and tally output, a momentary/latch selector and the DTMF detect output.
The remote line connect switch can be either momentary or latching in its action.
Balanced mic/line input – 10k balanced input selectable for 0dBu clean feed line, or microphone level with adjustable gain.
Balanced output – 0dBu low impedance balanced output, with output gain settings.
Record output – the conferencing output can be set via a jumper to give a mix of the caller and mic/line input signals for recording both sides of the telephone conversation.
Line limiter, bandpass filter and output noise gate with preset threshold providing low distortion audio.
Built in universal power supply between 90V AC and 250V AC, 47-63Hz, IEC mains input.
ETSI approval compliant with European PTT specifications.


Technical Specification For DHY-04

Analogue Audio I/O

Input Impedance – Line Mode (Clean Feed):
10kΩ balanced 0dB

Input Impedance – Conferencing:
10kΩ balanced 0dB

Input Impedance – Microphone Mode:
2kΩ balanced

Input Level Gain Range:
+6dB, 0dB, and -6dB adjusted by 3-position front panel switch, +10dB jumper

Microphone Level Gain Preset:
From 65dB to 35dB

Maximum Input Levels:
Line +26dBu, mic -24dBu

Clean Feed Limiting Input:
-4dBu for CTR21 setting, other values available *

Output Impedance – Line Out:
50Ω balanced floating 0dBu

Output Impedance – Conference/Record:
50Ω balanced floating 0dBu

Output Level Gain Range:
+6db, 0dB, and -6dB adjusted by 3-position front panel switch

Digital Audio I/O

Input Impedance:
110Ω ±20% balanced

Output Impedance:
110Ω ±20% balanced

Sample Frequency Range:
30 – 100kHz (i.e. including 32kHz, 44.1kHz, 48kHz, 64kHz, 88.2kHz & 96kHz)

Signal Level:
2V/7V peak to peak min/max

Analogue Input Level for Full Scale Digits:

Telephone Line

Bandwidth to Telephone Line:
250Hz – 4kHz, -3dB ref 1kHz

Telephone Line Impedance:
600Ω, 900Ω plus 14 other complex impedance circuits *

Rejection Ratio:
80-88dB on complex waveforms, reference peak level of 0dBFS

Ring Detector Sensitivity:
Off, 1, 2, 3, Off

Power Supply

Power to DHY-04, S & T
Universal 12W power supply: 90 to 250V AC; 47-63Hz; fused 1A


Mic/Line/AES-EBU Input:
XLR 3 pin female, with push-button mic/line selection

Line/AES-EBU Output:
XLR 3 pin male

Telephone Line:
RJ11 6/4 socket

Telephone Handset/Instrument:
RJ11 6/4 socket

Conferencing or Record Audio:
RJ45 socket

9-way D-type socket

RJ45 socket

RS232 Serial:
9-way D-type socket

IEC mains (CEE22)


Order Code

Front Panel Conversion Kit, DHY-04S to DHY-04

Front panel conversion kit, DHY-04 free standing to DHY-04S 19” (48cm) rack-mount front

Front panel conversion kit, DHY-04 or DHY-04S, to DHY-04T 19” (48cm) rack-mount front


4.5 cm x 21.8 cm x 17.5 cm (H x W x D)

2.2 kg




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STUDIO Telephone Interfaces Sonifex Telephone Hybrids Analogue HY-03