ADPCM was also used by Interactive Multimedia Association for development of legacy audio codec known as ADPCM DVI, IMA ADPCM or DVI4, in the early 1990s. Split-band or subband ADPCM. G.722 is an ITU-T standard wideband speech codec operating at 48, 56 and 64 kbit/s, based on subband coding with two channels and ADPCM coding of each. Vox Converter Online Converter WAV, MP3, OGG, M4A to Dialogic ADPCM.VOX File System Dialogic ADPCM or VOX is an audio file format, optimized for storing digitized voice data at a low sampling rate. VOX files are most commonly found in telephony applications. I have a video feed that sends me audio using the ADPCM codec. However, android only supports PCM format. How can I convert the ADPCM audio feed into a PCM audio feed? The answer to this may be similar to the answer to this question. I have successfully decoded the frame with this code. Aug 09, 2014 Video Game Sound Converter, or VGSC, is a program that can convert a range of video game audio formats to WAV.The conversion is actually handled by vgmstream, however VGSC wraps it with a simple UI and allows you to convert multiple files quickly and easily.
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PCM vs DPCM vs ADPCM-Difference between PCM,DPCM,ADPCM modulations
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This page on PCM vs DPCM vs ADPCM describes difference between PCM, DPCM and ADPCM modulation techniques.All these are pulse digital modulation techniques.
PCM
The short form of the Pulse Code Modulation is PCM. In PCM, the analog speech waveform is sampled and converted directly intoa multibit digital code by an Analog to Digital converter.The digital code is stored in the memory and which is later re-called for theplayback.
In this type of modulation, analog data is sampled and quantized before being represented to digital binaryform. Hence using PCM, continuous amplitude and continuous time signal waveform is converted into discrete amplitude and discrete timewaveform.
If there is a n bit quantizer and sampling rate is Fs then bit rate will be
Rb(bits/sec) = n * Fs
Sampling rate must be at a rate greater than or equal to nyquist rate to avoid aliasing.Higher the sampling rate easier is the reconstruction at the receiver.Bandwidth requirement is minimum Rb/2 and maximum Rb.
Signal to Quantization Noise Ratio for PCM for sinusoidal input is
SQNR (dB) = 6*n + 1.76, where n is bit of uniform quantizer.
DPCM
The short form of Delta Pulse Code Modulation is DPCM.In DPCM, a multi-bit difference value is stored.A bipolar D/A converter is used for playback to convert the successive difference valuesto an analog waveform.
Figures 1 and 2 depicts DPCM encoder and DPCM decoder block diagram.
This modulation scheme encodes difference in current as well as predicted values.
Simple block diagram of linear predictor used in DPCM is depicted in the fig3.
When the samples of a signal are highly correlated then we go for DPCM in order to save bandwidth or usingthe same bandwidth at higher data rate.
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Delta Modulation
It is a special case of differential PCM.It is called 1 bit DPCM as it transmits only one bit per sample.
In delta modulation problem of slope overload occurs if input is changing very fast that is :
| Δ/Ts | < | dm(t)/dt |
To overcome slope overload error we choose optimum size of Δ such that :
Δopt/Ts = | dm(t)/dt |max
For m(t) = Am*cos(2*π*fm*t)
Δopt/Ts = 2*π*fm*Am
The second problem occurs is hunting, which occurs when message is almost constant.
ADPCM
In adaptive delta modulation, step size is chosen in accordance with message signal sampled value to overcomeslope overload error and hunting.
If message is varying at a high rate then step size is high and if message is varying slowly then step size is small.
The short form of Adaptive Delta Pulse Code Modulation is ADPCM.In ADPCM, a difference value that has been mathematically adjusted accordingto the slope of the input waveform is stored. Bipolar D/A converter is used to convert the stored digital codeto analog for playback.
Figures 4 and 5 depicts ADPCM encoder and ADPCM decoder block diagram.
Refer advantages and disadvantages ofPCM >>,DPCM >> andADPCM >> techniques.
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Modulation types
BPSK -This page describes BPSK modulation technique with equation and constellation diagram.
QPSK -This page describes QPSK modulation technique with equation and constellation diagram.
QAM-This page describes QAM modulation technique with equation and constellation diagram.
MSK-GMSK MSK modulation,GMSK modulation and GMSK demodulation.
8PSK 8-PSK modulation or multilevel PSK or phase shift keying modulation technique.
BPSK vs QPSK -Difference Between BPSK and QPSK modulation techniques.
QPSK vs OQPSK vs pi/4QPSK-Difference between QPSK,OQPSK and pi/4QPSK modulation techniques
Differential Encoder and Decoder
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