Getting good tape from the telephone.
(For the purpose of this discussion it is assumed that we are trying to record broadcast quality audio, not merely recording for the record.
If you only want to have a client direct your voice recording in the studio, read this note. )
Telephone circuits are designed to deliver audio in the frequency range of 180 Hz - to 3.2kHz.
This is adequate for most speech, but a far cry from broadcast or studio audio.
The telephone works by the telephone company (telco)
providing approximately 48 volts of electricity to power the conversation and
generate touch tones between your telephone and their switch at the central
office (CO). The telephone company makes your phone ring with approximately 90 volts at 10 Hz.
This is something you don't want to personally experience and neither does your audio equipment.
A few more basics:
The telephone handset contains a transmitter and a receiver, which each are connected to the base unit by separate pairs of wires but does not contain a dial or touch tone pad. The base unit provides a network adapter that:
- Provides a reduced volume level from the transmitter back to the receiver so that the talker can hear themselves talking. (Sidetone)
- Combines the transmit and receive signals (4 wires) to the two wires leaving the base unit and connecting your telephone to the telephone network and ultimately the central office (CO).
- Routes the ring voltage to the ringer.
- Signals the CO that the phone is either on or off hook.
Reasons to connect:
You want to send audio down the phone line
You want to record audio from the telephone.
You want to do both at the same time.
Equipment For Connecting To The Phone?
A device that connects audio equipment to the telephone line.
If you only want to send audio down the phone line or record audio from the
telephone and you want to do only one thing at a time, then a simple
telephone COUPLER will do the job for you. A COUPLER provides a safe,
proper method of connecting to the telephone network. A coupler may or may
not include a hybrid in its design.
If you have ever been on an extension phone during a conversation to
someone some distance away, you will have noticed that the person speaking
on your end of the conversation is much louder than the person on the other
end. This volume difference is a problem if you are trying to record both
sides of the conversation in a balanced way.
This balance problem can be reduced by the use of a HYBRID, a circuit that
reduces the "send" volume (the talking on your end of the conversation) heard in the recording output by inverting its polarity and
adding the now out-of-phase signal back into the output to cancel out some
of the "send" volume. The better the hybrid works, the more you will pay
for it. The amount of reduction is referred to as separation and is
measured in - dbs. The greater the negative number the better the device.
Note that an analog hybrid will NOT cancel out ALL of the sender audio, but
usually enough to get the job done. The more expensive digital hybrids should effectively cancel
out nearly all of the sender audio.
Where do I connect?
There are two places that you can connect or "couple" into the telephone system.
- 1. Connect between the handset and the base unit of the telephone.
PLEASE NOTE: A handset, by definition, does NOT contain a dial or key pad.
If your handset does have a keypad, then you have a one piece phone (the cradle does not count for the purpose of this discussion, and you can NOT
use this technique.)
Connecting to a cell phone.
If you are on the go there may arise the need to record off your cell phone. From a sound quality side, the cell phone
does not produce a really good sound. Depending on your location and provider, the sound may be down right bad.
However, if you must, check out the JK Audio Daptor Two Wireless Phone Audio Interface
The Daptor 2 works on wireless phones have the 2.5 mm jack directly on the phone. Other phones may require a headset adapter which converts their proprietary connector into the 2.5mm jack.
Daptor Three is a simple, professional audio interface using Bluetooth Wireless Technology. Like its predecessor Daptor Two, this new version allows balanced and unbalanced connections to your cell phone.
|Before you make the decision to use a cell phone, don't forget that you may be dealing with not only poor audio quality
but there may be a serious delay problem to deal with also.|
The next consideration is do you have an analog or a digital
telephone system. Most all homes and many small businesses will use analog
telephone equipment. Other businesses may have a digital telephone system.
If you are not sure what you have, find out.
Couplers For Analog Telephones:
|Radio shack and others make a very inexpensive adapter
than connects between your handset and base unit. It has a switch for either
recording from, or sending audio to the phone. The audio connects through a phono
plug on a very short wire.
Show here with a phono to mini phone adapter. This device is great for recording "notes"
but may not work very well for "broadcast" audio, especially in high
rf fields. I carry one for insurance, but have never had to use it.
Other products that connect in the same fashion between the handset and the telephone base unit.
These devices provide more substantial connectors and other control functions that you may find useful.
|JK Audio THAT-1 and THAT-2 are both passive coupler devices (needs no external power) .
Both units provide a switch to shift between the handset and the audio input jack, and provide output of the audio from the telephone. The THAT-2 provides the output audio as both a mix of send and receive audio on both RCA and XLR jacks. You can continue to use the handset while
||The Microtel unit, a very useful and liked field tool has now been discontinued.
You may find one still on a dealers shelf if you look hard enough.
|The Excalibur HC-1 coupler allows connections to send or receive audio, or switch back to the handset.
(No other control functions.)
||The JK Audio QuickTap coupler offers access for recording both sides of a
conversation. (No other control functions.)
Couplers For Digital Telephones:
Digital telephones may use different types of microphones in the handset. This requires options
for adjusting the send volume.
- 2. Connect between the telephone and the wall jack. (RJ-11)
The standard home wall jack is an RJ-11. It uses the red and green wire in the normal 4 wire cable (JKT).
This is what you plug a home type single line phone into.
If your phone jack supports two lines, then you are using an RJ-14 which connects to the red, green, yellow and black wires in the cable.
To access the second line in an RJ-14 outlet, you must use a device designed for two line operation, or use a splitter or switch box to switch between.
An RJ-11 and a RJ-14 are the same jack, the only difference is the number of wires used to connect.
If you are trying to connect to a business
telephone system, you must determine what type of connection is in
use, is it analog or digital telephone system, and what it takes to interface your
equipment to the telephone system. If the system is digital, then
you will have to find someone that understands that particular
system. Both analog and digital systems can use an RJ-14 jack. Other digital systems use
a very similar looking plug with 6 or 8 wires.
(If you do much work in the field then the first option of connecting to the handset cord and the telephone base may make more sense.)
If you are connecting to a wall jack then there are two ways for a " coupler' to interact with the telephone line.
- The first is to bridge the line. This requires that a standard telephone be "off hook ".
This keeps the line open, but also allows the telephone microphone to be active (and pick up any noise in the room).
- The second is to seize the line. In this case the coupler acts for the telephone and keeps the line off hook.
It also disconnects the regular phone or allows you to hang up and let the device handle the audio.
(Don't forget to disconnect or hang up when you are through.)
Now assuming that we are dealing with an RJ-11 analog phone connection, Telos, Gentner and JK Audio make devices that will do the job.
Some are couplers only, others provide a Hybrid to balance the send and receive audio.
||The Gentner Hybrid
Coupler provides a pass through connection for a standard telephone, and allows for the coupler to bridge the line, or seize the line.
The Gentner also contains a passive hybrid providing approximately -10db of separation of caller and local audio. The Hybrid coupler is a passive device and requires no external power.
|The JK Audio Inline Patch coupler (hybrid) allows both bridge and seize mode. Audio outputs are provided for split audio (send and receive), or mixed.
Their hybrid is specked for 20db of separation. The Inline Patch is an active device and requires power.
|The TI 101 was originally made by Symetrix then sold
by Radio Systems, and now appears to be discontinued. This unit does require a mixer.
It also can be run in pairs to allow a guest and a caller.
The Comrex TCB-1 coupler is a passive device that will seize the line and allow for the sending of audio.
The Circuit Werkes AC-3 is a simple coupler hybrid that provides a separate unbalanced send and receive port. Will auto answer.
As with all technology, the digital hybrids are coming down in price. I recently checked
on well known units and found them priced below $600. While more pricey than the analog
units, the quality difference is an entire magnitude better.
||Comrex/Getner Digital - one of several
Connects between standard phone and the wall.
Will seize or bridge the line.
See also other units from Telos.
||Jk Audio Broadcast Host.
Connects between standard phone and the wall.
innkeeper PBX connects between phone and handset.
How to make a hybrid work.
To effectively make a telephone hybrid work, the studio end of the conversation should originate on a studio microphone.
(Not on the telephone handset.)
You can feed the studio microphone audio through one input of a mixer and use an aux buss to feed the telephone hybrid.
The audio output from the hybrid is connected to a second mixer input and is NOT fed back through the aux buss.
(The aux send provides what is called a mix minus for the hybrid)
You can then mix the two separate inputs to suit or record them to separate tracks to mix later.
You may wish to add a compressor between the caller output of the hybrid and the mixer input to help stabilize the volume variations as you would any other microphone. Some additional equalization can also be helpful.
Depending on how effectively your hybrid nulls the studio send audio, you may also want to "duck" the receive audio while the "studio" is talking. This can also be set up with a gate if you have the time to set all the adjustments.
You may also want to "duck" the studio microphone during long periods of caller audio
so that breathing noises do not go to tape. Obviously if the mixer and the studio talent are not one in the same, some degree of coordination will be necessary.
Some other thoughts.
For the home voice over studio...
If you only want to connect your personal studio to the telephone so that you can be directed while recording a script, you may want to
consider an analog hybrid if you can still find one to save money. You still have to deal with the problem of your mic send level
being hotter than the caller. The analog hybrid can take care of this. The analog "null" is not as great, but in this application
it is more than adequate.
Do you remember the Sprint pin drop commercials?
Many businesses today may use a lower quality bulk line for their
long distance calls. These lines tend to be nosier and have a more limited band width. If you encounter this condition, changing to a major carrier may give you a better quality line.
You will get better audio if the party you are calling is not using a cell phone or a cordless phone. Ask the to use
a wired phone if possible. Obviously you do not want them to use a speaker phone and avoid a headset
telephone. (The closeness of the mic to the mouth may create a distorted sound.)
The modular plug used between handset and base unit is not the same as the plug used between the base unit and the wall.
Always be certain that the person you are recording knows that they are being recorded.
Better yet, confirm that with them "on tape" just before you start.
A coupler provides a method of connecting to a telephone line.
A hybrid provides a method of balancing the send and receive audio.
Know your JR #s. RJ11=single line telephone circuit. RJ14=two lines in one jack.
The digital units are really worth the price difference if you can afford them.