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codec vs modem | difference between codec and modem

This page codec vs modem describes difference between codec and modem. Other difference between terms are also mentioned here.

Both of these devices are widely used in telecommunications for their specific roles. While Codec helps in compressing the data so that it will occupy less space or bandwidth. Before applying compression first input analog data is converted to digital form using coder part of codec. The modem helps in converting baseband information(i.e. voice(analog) or data(digital)) in the form such that it can be sent to certain distance without any errors or lose of data.

Codec-Coder Decoder

The full form of Codec is Coder-Decoder. Codec is the device which converts analog data to digital data and back. At the transmit end it converts analog data into digital coded form and at the receiver it converts the digital coded data to its original analog form.
For example, analog audio tones.

We find codec everywhere right from sound cards, voice mail system, scanners, video conferencing equipments and mobile phones, laptops etc.

Refer GSM AMR basics which describes how codec rate is changed based on C/I.

Modem-Modulator Demodulator

The full form of modem is modulator-demodulator. Modem is the device which modulates baseband information at transmit end and demodulates modulated signal at the receive end.

Input can be either in analog form or digital form. Carrier which is used for modulation purpose is always in analog form.

Modulator always converts any type of input data into analog form. Demodulator does the reverse.

Examples of analog modulation types are AM(Amplitude modulation), FM(Frequency modulation) and PM(Phase modulation), while examples of digital modulation types are ASK(Amplitude Shift Keying), FSK(Frequency Shift Keying) and PSK(Phase Shift Keying). Refer AM vs FM vs PM and ASK vs FSK vs PSK for more information.

More complex modulation techniques are available as part of modem device such as QPSK, 16QAM, 64QAM (6 bits/carrier) and 256QAM (8 bits/carrier) where in multiple bits are mapped over one single analog carrier. More example, in QPSK 2 bits are represented by one analog carrier frequency, in 16QAM 4 bits are mapped to 1 carrier and so on. Refer QPSK modulation and QAM modulation for more information.

Following table mentions various modem standards.

Modem standards Description
V.22 1200-2400 baud/bps (FM)
V.32, V.32bis full duplex at 9600 bps (2400 baud at QAM)
V.32bis uses TCM to achieve 14,400 bps.
V.34 • for phone networks using digital transmission beyond the local loop.
• 59 combinations of symbol rate and modulation technique.
• symbol rates 3429 baud. Its bit rate is up to 28,800 bps (TCM-8.4).
V.34+ up to 33.6 kbps with TCM-9.8
V.42bis uses Lempel-Ziv encoding and attains 3.5:1 to 4:1.
V.42bis compression can be added to almost any modem standard effectively tripling the data rate.
V.90 allows 56 kbps (download) and 33.6 kbps (upload)
V.92 allows 56 kbps (download) and 48 kbps (upload), it uses PCM for both download and upload

Useful Links

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