Side by Side: Telephone Hybrids

November 1, 2011

It''s hard to imagine creating great radio without listener interaction, and the classic form of interaction is the telephone. The basic technology of an analog telephone line (plain old telephone service, or POTS) hasn''t changed much over the years, but the ability to send and receive high-quality audio through that phone line certainly has.

Digital technology has given the telephone hybrid outstanding audio specifications in send and receive audio isolation, as well as the ability to adapt for ever-changing telephone line conditions. Digital audio processing has also improved the sonic performance.

While newer technology for telephony exists, the POTS line is still in common use. We picked four popular single-line telephone hybrids to compare.

ModelAEQ TH-03Comrex DH20JK Audio Inkeeper 1xTelos Hx1
Price$895$995 $795 $795
Incoming Line CapacityOneOneOneOne
HybridsDigital with Electronic Echo SupressionDigitalDigitalDigital
Audio I/OXLR-3 connectors, program in/outAnalogAnalogAnalog (AES optional)
Audio input (send)Analog or Digital AES or EBUXLR, mic/line selectableMic/line balanced XLRXLR, mic/line selectable
Audio output (receive)Analog or Digital AES or EBUXLRBalanced XLR (2)XLR
Send processing250Hz frequency extender, which enhances bass frequenciesNoneInput limiterSample rate conversion, high-pass filter, frequency shifter, AGC/limiter
Receive processing250Hz frequency extender, which enhances bass frequencies. Also includes auto gain controlAGC, downward expander, caller control (ducking), high/low pass filtering, echo cancellationDual convergence echo cancellation, AGC, presence equalization, duckingHigh-pass “hum” filter, smart AGC/platform leveler, noise gate, caller ducking, Telos'' Digital Dynamic Equalization 3-band adaptive spectral processor, sample rate conversion
Input Analog-to-digital converter resolution24-bit D/A converter resolution16-bit16-bit20-bit
Output digital-to-analog-converter resolution24-bit D/A converter resolution16-bit16-bit24-bit
Frequencey response300Hz-4kHz (extender off)/50Hz-3,750Hz (extender on)250Hz to 3.5kHz100Hz to 3.4kHz200 to 3.4kHz
Signal to NoiseAbsolute noise: TX <-66dBm. RX <-68dBm. Cross-talk lower than absolute noise>56dB52dB (receive audio during call)>90dB
Analog telephone line connectivityRJ-11, standard POTS line, 600 ohms Z.RJ-11 connector, POTS line or analog extension from a PBX or dry lineRJ-11Universal POTS interface for worldwide application, programmable loop current, auto-answer with selectable ring count, worldwide disconnect signal detection
Other modelsTH-03.1 A (analog), TH-03.1 D (digital), TH-03.2 AA (two-line analog), TH-03.2 AD (two-line analog/digital), TH-03.2 DD (two-lines digital)DH22 (two-line), DH30 (added functions)Tabletop version available, Inkeeper 2 (two-line), Inkeeper 4 (four-line), Inkeeper LTDHx2 (two-line)
Weight6lbs 3oz6.35lbs5.7lbs5lbs
Power90-250Vac, 50/60Hz, 20WIEC Type, auto adjusting 100-240Vac, 2A, 50/60Hz, 30W120-240Vac100V-240V, internal, auto-switching