Side by Side: Telephone Hybrids
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.
|Model||AEQ TH-03||Comrex DH20||JK Audio Inkeeper 1x||Telos Hx1|
|Incoming Line Capacity||One||One||One||One|
|Hybrids||Digital with Electronic Echo Supression||Digital||Digital||Digital|
|Audio I/O||XLR-3 connectors, program in/out||Analog||Analog||Analog (AES optional)|
|Audio input (send)||Analog or Digital AES or EBU||XLR, mic/line selectable||Mic/line balanced XLR||XLR, mic/line selectable|
|Audio output (receive)||Analog or Digital AES or EBU||XLR||Balanced XLR (2)||XLR|
|Send processing||250Hz frequency extender, which enhances bass frequencies||None||Input limiter||Sample rate conversion, high-pass filter, frequency shifter, AGC/limiter|
|Receive processing||250Hz frequency extender, which enhances bass frequencies. Also includes auto gain control||AGC, downward expander, caller control (ducking), high/low pass filtering, echo cancellation||Dual convergence echo cancellation, AGC, presence equalization, ducking||High-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 resolution||24-bit D/A converter resolution||16-bit||16-bit||20-bit|
|Output digital-to-analog-converter resolution||24-bit D/A converter resolution||16-bit||16-bit||24-bit|
|Frequencey response||300Hz-4kHz (extender off)/50Hz-3,750Hz (extender on)||250Hz to 3.5kHz||100Hz to 3.4kHz||200 to 3.4kHz|
|Signal to Noise||Absolute noise: TX <-66dBm. RX <-68dBm. Cross-talk lower than absolute noise||>56dB||52dB (receive audio during call)||>90dB|
|Analog telephone line connectivity||RJ-11, standard POTS line, 600 ohms Z.||RJ-11 connector, POTS line or analog extension from a PBX or dry line||RJ-11||Universal POTS interface for worldwide application, programmable loop current, auto-answer with selectable ring count, worldwide disconnect signal detection|
|Other models||TH-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 LTD||Hx2 (two-line)|
|Power||90-250Vac, 50/60Hz, 20W||IEC Type, auto adjusting 100-240Vac, 2A, 50/60Hz, 30W||120-240Vac||100V-240V, internal, auto-switching|
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