adpcm and an 8 bit uC

EDAboard.com Forum Index -> Microcontrollers -> adpcm and an 8 bit uC

Author

Message

lollobrigido

Joined: 13 Dec 2002
Posts: 149
Helped: 1
Location: Italy

12 Dec 2003 12:54 adpcm 8bit

I'm searching for ADPCM algorithm that get 8bit stream data and encode it in 'n' bit (with n < 8 obviously Razz

). I found only algorithm that get 16 bit stream data and encode in 4 bit, but I've a uC that has an ADC of 8 bit and I think the usage of 16 bit algo is fool.
Thx for any answer
Lollo

Google
AdSense
Google Adsense

12 Dec 2003 12:54 Ads

klug

Joined: 04 Jul 2002
Posts: 446
Helped: 5

12 Dec 2003 16:24 8bit adpcm

Quote:

Thx for any answer

Ok, some answer Smile

I have made ADPCM decoder with 8-bit DAC. AFAIK, there is no big reason to change algorithm from 16-bit to 8-bit - as, anyway, you will have 4 bits of data on memory. There is automatic scale changing on ADPCM algorithm. Also, there was no distortions at all - After making sequential encoding and decoding of voice wav file there was none bit changing. But you will get distortions if you decrease variables size in routine.

artem

Joined: 22 May 2003
Posts: 1652
Helped: 91
Location: Turan

12 Dec 2003 16:40

read this excerpt :
"ADPCM

Adaptive Differential Pulse Code Modulation ADPCM (G.721) allows for the compression of PCM encoded input whose power varies with time. Feedback of a reconstructed version of the input signal is subtracted from the actual input signal, which is then quantised to give a 4 bit output value. This compression gives a 32 kbit/s output rate. This standard was recently extended in G.726 , which replaces both G.721 and G.723 , to allow conversion between 64 kbit/s PCM and 40, 32, 24, or 16 kbit/s channels. G.727 is an extension of G.726 and issued for embedded ADPCM on 40, 32, 24, or 16 kbit/s channels, with the specific intention of being used in packetised speech systems utilizing the Packetized Voice Protocol (PVP), defined in G.764.

The encoding of higher quality speech (50Hz-7kHz) is covered in G.722 and G.725 , and is achieved by utilizing sub-band ADPCM coding on two frequency sub-bands; the output rate is 64 kbit/s. "

o what you are looking for is the ITU-T standard .