audio compression - Feature Requests - CHDK Forum  

audio compression

  • 5 Replies
  • 3039 Views
audio compression
« on: 12 / October / 2008, 15:05:21 »
Advertisements
i would love to have the ability to turn off the audio compression or have access to it's parameters for adjustment.  i use the audio recording function in my sd870 often for live music recording.  it's really handy to snap some shots and record a song with one device, but the extreme audio compression sounds horrible.  i think the microphone circuit has a decent enough frequency response and noise floor, but the audio compression really does bad things to the recorded sound.   

*

Offline reyalp

  • ******
  • 12864
Re: audio compression
« Reply #1 on: 12 / October / 2008, 17:40:14 »
I'm not sure about the sd870, but the earlier cams just record lossless PCM. The low quality is due to the low sample size and rate. These are likely hardware limitations, as there would be no reason for canon to spec 16 bit audio when they only ever record 8 bit. Nor would they spend a lot on the quality of the rest of the audio hardware.
Don't forget what the H stands for.

*

Offline PhyrePhoX

  • *****
  • 2254
  • make RAW not WAR
    • PhyreWorX
Re: audio compression
« Reply #2 on: 12 / October / 2008, 18:15:16 »
on s-series you can set the quality.

Re: audio compression
« Reply #3 on: 13 / October / 2008, 13:21:29 »
I'm not sure about the sd870, but the earlier cams just record lossless PCM. The low quality is due to the low sample size and rate. These are likely hardware limitations, as there would be no reason for canon to spec 16 bit audio when they only ever record 8 bit. Nor would they spend a lot on the quality of the rest of the audio hardware.

the audio on my camera is 16 bit 44.1k, which is fine really.  it's the audio compression (not file compression) that is screwing up the sound.  the audio compression brings up the noise floor and creates a squashed, pumping sound. 
 
« Last Edit: 13 / October / 2008, 13:23:45 by travis »


*

Offline fudgey

  • *****
  • 1705
  • a570is
Re: audio compression
« Reply #4 on: 13 / October / 2008, 15:27:26 »
From ixus860_sd870/sub/100c strings:
ff8547c0 AudioIC_WM1400.c

Yep, that's definitely a different audio chip, my a570is has AudioIC_LA74310LP.c. LA74310LP is a Sanyo chip which also includes a driver for the video output jack. Google doesn't give me much of anything about WM1400, could be a customer specific IC or that may not be it's usual commercial name.

WM1400 is in at least ixus70/sd1000, ixus860/sd870, ixus950/sd850 and ixus960/sd950.
LA74310LP is in at least a450, a460, a560, a570, a650, a720, sx100.
s5is and tx1 have AudioIC_AK4646, a stereo codec by Asahi Kasei.

Also, I can't find any strings that would refer to AGC or ALC. The chip is probably entirely responsible of this dynamic compression you're suffering from, but it's quite likely that the firmware can configure it. Having a datasheet of the chip would be essential, then it would be possible to find where it's configured (strings such as SoundRecordController.c could lead the way). In both LA73210LP and AK464 their ALC features can apparently be switched off by software.

Re: audio compression
« Reply #5 on: 13 / October / 2008, 20:13:03 »
From ixus860_sd870/sub/100c strings:
ff8547c0 AudioIC_WM1400.c

Yep, that's definitely a different audio chip, my a570is has AudioIC_LA74310LP.c. LA74310LP is a Sanyo chip which also includes a driver for the video output jack. Google doesn't give me much of anything about WM1400, could be a customer specific IC or that may not be it's usual commercial name.

WM1400 is in at least ixus70/sd1000, ixus860/sd870, ixus950/sd850 and ixus960/sd950.
LA74310LP is in at least a450, a460, a560, a570, a650, a720, sx100.
s5is and tx1 have AudioIC_AK4646, a stereo codec by Asahi Kasei.

Also, I can't find any strings that would refer to AGC or ALC. The chip is probably entirely responsible of this dynamic compression you're suffering from, but it's quite likely that the firmware can configure it. Having a datasheet of the chip would be essential, then it would be possible to find where it's configured (strings such as SoundRecordController.c could lead the way). In both LA73210LP and AK464 their ALC features can apparently be switched off by software.


i did some googling and found references to wm1400 in the datasheet for wolfson wm8974 and wolfson alc sheet.  i also took a look at wolfson's audio codec products and wm8974 is the only one that fits the description:  mono, no headphone driver, and dsp alc. 

alc sheet:  http://www.wolfsonmicro.com/uploads/documents/en/WAN0178.pdf
wm8974 sheet:  http://www.wolfsonmicro.com/uploads/documents/en/WM8974.pdf
wolfson audio codecs:  http://www.wolfsonmicro.com/productListings/codecs/

 

 

Related Topics