Support and General Use > Audio Playback, Database and Playlists
Enabling 24bit-44.1/48/88.2/96khz playback - iAudio and others?
lazpete:
Oh, didnt know that.
Well, guess a resampling is in order then.
mcmurray:
I've done some reading on the TI AIC23B audio chip used in the X5 and it seems that with a clock frequency of 11.2896Mhz the only sample rates available are 44.1 and 88.2 Khz. Not much use since most 24bit material I've come across is either 48khz or 96khz. Bugga.
I'll look in to the iPod as I heard it may be 24bit capable.
preglow:
--- Quote from: mcmurray on October 15, 2007, 01:55:59 AM ---I will try and contact preglow and see what needs to be done.
--- End quote ---
I'll just reply here so other people can read the reply too.
Saratoga is correct in saying that everything is truncated (or dithered, if you have that enabled) to 16 bits. This operation can be changed to other bit depths rather easily in dsp.c, but there are other sides to the problem too:
1. currently, the pcm buffering layer stores everything as 16 bit ints in the queue where the audio is stored before being sent to the DAC. I'm not sure how hard it'd be to change this to 32 bit data.
2. we use DMA for transfering audio to the DAC. Using DMA imposes a limit of maximum 16 bits on us, so we'll need another interrupt based driver for transfering sizes above 16 bits. This driver will be slower than the current DMA one, but I'm not sure how much.
mcmurray:
Thanks for chiming in preglow. Just one stupid question, why is the DMA transfer limited to 16bits?
saratoga:
--- Quote from: mcmurray on October 15, 2007, 01:55:59 AM ---My 24bit material is from DVD-Audio and DVD-Video rips, also I have been listening to some taped live music in 24bit format (see www.flacmusic.com) which sounds amazing and more is becoming available every day. I also intend to rip my vinyl collection to 24bit FLAC.
--- End quote ---
Be careful here. No concert recording is going to have even close to 16 bit resolution, so these should probably be kept at 16 bit. Likewise, vinyl cannot do 16 bit either, so 24 bit is silly. DVD-V is just AC3, DTS or MP2 lossy compressed audio, so theres no point in 24 bit playback. That really just leaves DVD-A, and even that is not always 24 bit.
--- Quote from: mcmurray on October 15, 2007, 01:55:59 AM ---24bit doesn't just provide a better snr than 16 bit, it also provides more resolution (16777216 discrete levels for 24bit as opposed to 65536 levels for 16 bit i.e. much closer to analogue performance), and a higher signal to quantization distortion ratio.
--- End quote ---
These are all the same thing. The only improvement is that the SNR is no longer restricted to ~ 100dB. However, this isn't really a limitation, as you can't really hear any wider range, unless you're a child in an anechoic chamber.
--- Quote from: mcmurray on October 15, 2007, 01:55:59 AM ---Even though the SNR may not be limited by 16bit, the higher resolution will still be noticable (in the same way that vinyl provides very good resolution in spite of poor SNR).
--- End quote ---
Resolution and SNR are essentially the same thing. Vinyl provides poor SNR and poor resolution.
--- Quote from: mcmurray on October 15, 2007, 01:55:59 AM ---Im using and listening to ripped albums at 24 bit 96 khz in flac on my sansa e200. Large but fantastic...
--- End quote ---
You're listening to our somewhat poor resampler. You'd get much higher fidelity out of CD audio I'm afraid. It seems to me you really need to sit down and ABX some of your tracks at 24 bit and at 16 bit. I think you'll be surprised what the difference really is if you think our resampler sounds "fantastic" :)
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