Adpcm Converter
Adaptive Differential Pulse Code Modulation (ADPCM) is a lossy compression format that is implemented for XAudio2 to provide additional features for specifying the size of the compression sample block. With a lossy compression format some data is altered and lost during compression. ADPCM can achieve compression ratios of up to 4:1.
It's very good for real-time measurement, the use of this software is very professional. Softe WAV Converter is a software for WAV (PCM, IMA ADPCM, aLaw, uLaw) to MP3 FLAC WMA APE OGG AAC M4A conversion and audio to WAV (PCM, IMA ADPCM, aLaw, uLaw) format conversion. Adaptive Differential Pulse Code Modulation (ADPCM) is a lossy compression format that is implemented for XAudio2 to provide additional features for specifying the size of the compression sample block. With a lossy compression format some data is altered and lost during compression. ADPCM can achieve compression ratios of up to 4:1. ACM Converter 3.2 is software that allows you to convert ACM and PCM WAV files from one format to another. Add the audio files you wish to convert by adding them from the dialog box or by dragging.
The implementation of ADPCM for XAudio2 provides additional features to specify the size of the compression sample block. ADPCM enables the audio designer to choose a setting that is an appropriate compromise among size, quality, and resolution (for placing loop points).
XAudio2 uses a modified version of the Microsoft ADPCM codec that supports the extended data formatting required to provide custom sample block sizes. For this reason, XAudio2 audio data cannot be played by audio engines that do not support this version of the ADPCM codec.
Note
Looking for a WAV to ADPCM2 audio converter SDK. Preferably written in.NET, though ActiveX or standard DLL (that can be PInvoked from.NET) is suitable as well. The ADPCM2 format was created by OKI and is used in some mobile devices, and shouldn't be confused with the ADPCM or VOX formats, which I believe differ slightly.
Currently, ADPCM compression is only available for Windows, including XNA Game Studio Express for Windows deployments.
ADPCM Encoding
Audio data is encoded to ADPCM using the AdpcmEncode command-line tool.
AdpcmEncode
In order to encode audio files as ADPCM for use with XAudio2, use the AdpcmEncode command-line tool.
ADPCM Decoding
Software decoding of ADPCM is supported in XAudio2.
XAudio2
In order to use ADPCM encoded data in XAudio2, you need to initialize a ADPCMWAVEFORMAT structure with ADPCM specific values, and pass it as an argument to IXAudio2::CreateSourceVoice when you create a source voice. For an example of loading and playing a sound in XAudio2, see How to: Play a Sound with XAudio2.
SamplesPerBlock
ADPCM compression works by separating the waveform into blocks, and predicting the variation of the waveform samples within each block. The size of the blocks is measured in samples. The smallest block size is 32 samples, and the highest is 512 samples.
Larger blocks allow better compression, which results in smaller file sizes, but at the expense of sound quality and resolution for aligning loop points.
In general, modifying the SamplesPerBlock value results in these tradeoffs:
| If SamplesPerBlock.. | File Compression | Sound Quality | Loop Point Resolution |
|---|---|---|---|
| Increases (up to max 512) | Increases | Decreases | Decreases |
| Decreases (down to min 32) | Decreases | Increases | Increases |
Restrictions
Because ADPCM uses sample blocks that are aligned one after the other, a wave compressed with ADPCM may have an unfinished, partial block at its end. The ADPCM decoder generates silence for the remainder of this partial block, which keeps the wave from looping seamlessly.
The value of the SamplesPerBlock parameter affects the resolution with which you can align wave data and loop points.
If you try to apply compression to a non-aligned wave, you will get an error or a warning depending on whether the wave is used in any looping play events. You cannot compress a wave used in any looping play events. Remove it from the looping play events, and re-apply compression.
If you use the wave exclusively in non-looping mode, the sample block alignment restriction does not apply.
ADPCM File Structure
An ADPCM file is a standard RIFF file with the following chunk types.
| Chunk FCC | Description |
|---|---|
| RIFF | Standard RIFF chunk containing a file type with the value WAVE in the first four bytes of its data section and the other chunks in the file in the remainder of its data section. |
| fmt | Contains the format header for the ADPCM file. The data in this chunk corresponds to a ADPCMWAVEFORMAT structure. |
| data | Contains the encoded ADPCM audio data. When you use ADPCM in XAudio2, you need to read the contents of the data chunk into a buffer, and pass it to a source voice as the pAudioData member of an XAUDIO2_BUFFER structure. You don't need to byte swap the contents of the data chunk. |
| smpl and wsmp | Optional chunk types containing the looping information for the ADPCM file. When you use ADPCM in XAudio2, the values contained in the smpl or wsmp chunks are used to populate the LoopBeginLoopLength and LoopCount members of the XAUDIO2_BUFFER structure. On the Xbox 360, you need to byte swap the data loaded from a smpl chunk to account for the endianness difference between Windows and Xbox 360. |
Related topics
PCM vs DPCM vs ADPCM-Difference between PCM,DPCM,ADPCM modulations
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.
Adpcmwaveformat
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.
Adpcm Converter
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.
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.
Adpcm Compression Ratio
Figures 4 and 5 depicts ADPCM encoder and ADPCM decoder block diagram.
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Refer advantages and disadvantages ofPCM >>,DPCM >> andADPCM >> techniques.
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
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