. Resolution/sample size: This parameter specifies the amount of data used to represent each discrete amplitude sample.
The most common values are 8 bits (1 byte), which gives a range of 256 amplitude steps, or 16 bits (2 bytes), which gives a range of 65536 amplitude steps. Other sizes, such as 12 and 24 bits, are occasionally seen. Endian-ness: When more than one byte is used to represent a PCM sample, the endian-ness (big or little) must be known. Due to the widespread use of little-endian Intel CPUs, little-endian PCM tends to be the most common byte orientation. Signed-ness: It is not enough to know that a PCM sample is, for example, 8 bits wide. Whether the sample is signed or unsigned is needed to understand the range.
If the sample is unsigned, the sample range is 0.255 with a centerpoint of 128. If the sample is signed, the sample range is -128.127 with a centerpoint of 0. If a PCM type is signed, the sign encoding is almost always 2's complement. In very rare cases (most notably on the Sega CD video game console), signed PCM audio is represented as a series of sign/magnitude coded numbers.
Channels/Interleaving: If the PCM type is monaural, each sample will belong to that one channel. If there is more than one channel, the channels will almost always be interleaved: Left sample, right sample, left, right, etc., in the case of stereo interleaved data.
In some rare cases, usually when optimized for special playback hardware, chunks of audio destined for different channels will not be interleaved. Frequency/sample rate: This parameter measures how many samples/channel are played each second.
Sep 17, 2009 - Missing Intel IMA ADPCM (11). Plug-ins for Windows Media Player http://www.microsoft.com/windows/windowsmedia/player/plugins.aspx. Windows Media Player cannot play the file (or cannot play either the audio or video portion of the file) because the Microsoft ADPCM Format (2) codec is not installed.
Frequency is measured in samples/second (Hz). Common frequency values include 8000, 11025, 16000, 22050, 32000, 44100, and 48000 Hz. The most common PCM formats revolve around the most commonly available hardware: Little-endian Intel CPUs. Microsoft multimedia files (WAV/AVI/ASF) designate PCM audio with format 0x01. If the WAVEFORMAT header indicates 8 bits/sample, the data will be unsigned.
If the header indicates 16 bits/sample, the data will be signed and little-endian. Stereo data will be interleaved, LRLRLR. Frequency will be specified in the WAVEFORMAT header. Apple Quicktime files with audio will have an audio stsd audio that will specify audio fourcc, frequency, bits/sample, and number of channels. The signed-ness of PCM data is indicated by the audio fourcc. 'raw ' (note the space needed to complete the fourcc) means unsigned data.
If 'raw ' data is 16 bits/sample, it will always be little-endian. 'twos' indicates 2's complement, big-endian data. 'sowt' ('twos' backwards) indicates 2's complement, little-endian data. Stereo data is always interleaved. A quick note about some sample rate oddities you may encounter in certain vintage multimedia files (from the early-, mid-, and even late-1990s): You may see sample rates of 11127 and 22254. Where did these numbers come from?
The original Sound Blaster was the first commodity PC sound card with a digital-analog converter (DAC) for digital audio playback. When programming the Sound Blaster DAC, it is necessary to program the sample rate by sending a 2's complement signed byte according to this formula. Interplay DPCM requires a 256-element delta table for encoding and decoding. The delta table is listed in Appendix A.
For each chunk of DPCM data in an Interplay MVE file, the first 2 bytes comprise an initial predictor stored in a signed, 16-bit, little-endian format. If the file is stereo, that predictor is treated as the left channel initial predictor and the next 2 bytes comprise the right channel initial predictor. The remainder of the bytes are indices into the delta table. For each byte, fetch a signed delta and apply it to the appropriate predictor (stereo data is interleaved LRLR.).
Saturate the predictor to a signed 16-bit range after each delta is applied. Predictor: This is either initialized from the data chunk preamble specified in the format or is initialized to 0 at the start of the decoding process step index: Similar to the initial predictor, this variable is initialized from the data chunk preamble or set to 0 at the start of the decoding process step: This variable is initialized to imasteptablestepindex The encoded IMA bitstream is comprised of a series of 4-bit nibbles. This means that each byte represents 2 IMA nibbles. The specific data format will dictate whether the stream is decoded top nibble first or bottom nibble first, and whether there is stereo interleaving within the IMA nibbles. For this discussion, imagine the IMA bitstream as a series of nibbles representing a single audio channel. Bytes 0-1: initial predictor (in little-endian format) for left channel byte 2: initial index for left channel byte 3: unknown, usually 0 and is probably reserved bytes 4-5: initial predictor (in little-endian format) for right channel byte 6: initial index (for right channel) byte 7: unknown, usually 0 and is probably reserved The remaining bytes in the chunk are the IMA nibbles.
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The first 4 bytes, or 8 nibbles, belong to the left channel and the next 4 bytes belong to the right channel. This interleaving continues until the end of the chunk. Bytes 0-1: initial predictor (in little-endian format) for left channel byte 2: initial index for left channel byte 3: unknown, usually 0 and is probably reserved bytes 4-5: initial predictor (in little-endian format) for right channel byte 6: initial index (for right channel) byte 7: unknown, usually 0 and is probably reserved The initial left and right channel predictors are placed directly into the output as the first PCM samples for each channel. The remaining bytes in the chunk are the IMA nibbles. For each byte, the top nibble (bits 7-4) corresponds to the left channel and the bottom nibble corresponds to the right channel. Some Sega Saturn game CDs contain AVI files which store audio using the Duck DK3 ADPCM algorithm.
These AVI files report format 0x62 as their audio codec. DK3 ADPCM data can be decoded using the same tables as are used to decode IMA ADPCM data while using a slightly modified variant of the IMA ADPCM algorithm. The name DK3 apparently comes from the fact that 3 ADPCM nibbles decode to 4 16-bit PCM samples, in contrast to Duck's DK4 ADPCM algorithm, in which 4 ADPCM nibbles decode to 4 16-bit PCM samples. get next ADPCM nibble in stream. update sum channel predictor and index using nibble. get next ADPCM nibble in stream.
update diff channel predictor and index using nibble. diff value = (diff value + diff predictor) / 2.
next left channel PCM sample = sum channel + diff value. next right channel PCM sample = sum channel - diff value. get next ADPCM nibble in stream. update sum channel predictor and index using nibble. next left channel PCM sample = sum channel + diff value. next right channel PCM sample = sum channel - diff value.
A different, smaller step table is used (refer to Appendix A for the table). The table contains 49 values ranging from indices 0.48. The predictor is always initialized to 0 at the start of decoding.
The index is always initialized to 16 at the start of decoding. When the index is modified by the ADPCM delta, it should be clamped within the 0.48 range, rather than 0.88. When the diff is applied to the predictor, it should be clamped within a signed 12-bit range (-2048.2047) rather than a signed 16-bit range. The output samples are 12 bits in resolution and should be scaled as necessary. See Appendix A for the modified IMA tables. Bytes 0-1: initial predictor for left channel bytes 2-3: initial predictor for right channel bytes 4-5: initial index for left channel bytes 6-7: initial index for right channel The first half of the remaining bytes of the chunk are the left IMA nibbles which the second half are the right of the remaining bytes are the right IMA nibbles.
For example, if an entire chunk of stereo 4xm audio is 108 bytes (decimal), the first 8 bytes are the preamble, the next 50 bytes are left channel nibbles and the final 50 bytes are right channel nibbles. As in monaural data, bytes are decoded bottom nibble first (bits 3-0), then top nibble. Byte 0 left channel block predictor (should be 0.6) byte 1 right channel block predictor (should be 0.6) bytes 2-3 left channel initial idelta bytes 4-5 right channel initial idelta bytes 6-7 left channel sample 1 bytes 8-9 right channel sample 1 bytes 10-11 left channel sample 2 bytes 12-13 right channel sample 2 Following the preamble, the left and right ADPCM samples are interleaved within each byte. The upper nibble (bits 7-4) contains the left channel ADPCM code and the lower nibble contains the right channel ADPCM code. ADPCM reference implementation:.
XAnim:. QuickTime4Linux:. libsndfile:. duck.exe Truemotion (and ADPCM) player:.
Apple Developer Connection Technical Note TN1081: Understanding The Differences Between Apple And Windows IMA-ADPCM Compressed Sound Files:. Command & Conquer Technical Page (for Westwood Studios ADPCM):. SMJPEG Library:. Dialogic ADPCM Algorithm:. The Bit Rate Reduction Sound Encoding Scheme, as interpreted by Butcha:. Id Software's.RoQ Video File Format:. Interplay MVE File Format:.
CRI ADX tools:. How do I convert to/from mu-law format?. SoX Sound eXchange:. xine Multimedia Player.
Hi, I know for sure that i’m not the first person to have this problem, but i am having real trouble finding a fix to it.
The problem is that i am missing the MS ADPCM (0x0002) audio codec in Windows XP and as such i can get beautiful pictures with my video files, but no sound. I know that this codec should come with Windows, but for whatever reason i don’t have it on my version. I have checked the Win32 directory and the msadp32.acm file, which i believe is the codec file, is there.
So if anyone thinks they can help solve my problem and stop me pulling the rest of my hair out then i would be very greatful.