Support and General Use > Audio Playback, Database and Playlists

-24db Precut Sound Quality on Rockboxxed iPod?

<< < (6/10) > >>

safetydan:
The Rockbox DSP does things in the following order:

1. Receive PCM data from the codecs in whatever format. This is converted to an internal 32-bit fixed point format.
2. Apply a gain to the data. This gain is the combination of the replay gain and the software equalizer precut. All it is is a multiply of each sample of the PCM data.
3. Resample the data.
4. Apply crossfeed if enabled.
5. Apply the software equalizer if enabled.
6. Apply the software tone controls if enabled.
7. Apply channel processing if enabled (mono/stereo/karaoke etc).
8. Clip the samples back down to 16-bit for sending to the DAC.

Not quite sure if I have a point in all that, but I figured I'd try and write up what Rockbox actually does. May or may not be accurate but is based on reading the source.

Andhyka:
Ok I'll just make everything short. Compress is just anti-thesis of normalize. You compress signal from maximum SNR to reduced SNR, while you normalise signal from reduced SNR to maximum SNR.

And here's what happened during audio processing in Rockbox.

Rockbox:

SOURCE 16bit -> -24db precut (4bit) -> DSP 12bit in 32bit -> DAC 12bit in 16bit -> MUFFLED SIGNAL

What I thought originally on first post:

SOURCE 16bit -> DSP 16bit in 32bit -> -24db compress (4bit) -> DSP 16bit in 28bit/32bit -> DAC 16bit in 21bit/24bit -> CLEAN SIGNAL
(Provided there's such function called "compress" and the ADC/DAC accepts 24bit signal)

Llorean:
As has been clearly stated by me: lowering the gain by 24db will result in the same amount of lost data whether you do it in 32-bit or 16-bit. As was stated by Dan, the gain adjustment happens after the 32-bit conversion. You're basing the loss of 4-bits on a random statement by one person, and ignoring the mathematical implications. If you increase from 16-bit to 32-bit, the value of bits are changed entirely.

Please, if you want to make a statement as to what is happening, rather than what you mistakenly think is happening, back it up by research. His statement comes straight from the Rockbox source code, for example.

Andhyka:
I'm not a developer and audio expert in this regard, and I don't know what happened in the inner workings of Rockbox. I'm just trying to figure out everything without good background on those areas (so as to use my Rockbox'ed iPod to maximum potential).  >:(

If you have any recommended settings I can directly use to do so. Let me know.

Peace.

Llorean:
It's basic math: If something removes 4 bits at 16-bit, it removes 8 bits at 32-bit. If it also only removed 4 bits at 32-bit, then why couldn't we do it simply by removing 2 bits at 16-bit, and never do the conversion? It's all math, and it's all determinate. If you look at it that way, it's absolutely clear that the same determinate mathematical operation cannot have two different results when applied to the same data, now can it?

Navigation

[0] Message Index

[#] Next page

[*] Previous page