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Audio Playback, Database and Playlists / Re: Bit depth, Dithering, and the Rockbox audio path

« Last post by saratoga on Today at 06:31:52 PM »

It doesn't matter what you do if you're converting down to 24 bit, it'll have no effect. If you were converting to something lower I would do it each time.

Zero padding to 32 bits is probably meant to make it less annoying to send, since natively most hardware doesn't support 24 bit operations.

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Audio Playback, Database and Playlists / Re: Bit depth, Dithering, and the Rockbox audio path

« Last post by dconrad on Today at 06:10:50 PM »

I don't think 32 bit flac exists, but ignoring that, since these are 32 bit processors without floating point everything is done natively on 32 bit.  At the end of processing it is converted to 16 bit in order to double the PCB buffer capacity and because most hardware expects 16 bit samples.  For the most part smaller than 32 bit samples are not used because they're slower on most of our hardware.

So that confirms my question that the current audio path only goes down to 16-bit once?

You only dither when reducing bit depth, never increasing.  In this case though its not needed since nothing can actually decode a 24 bit sample, so the dither would be lost anyway.

Right. So, in my question, I am reducing bit depth a second time (from 32 to 24), so is it (theoretically) advisable to dither a second time?

Most real world hardware has somewhere between 14 to 18 bits, so values larger than 24 bit do not make sense.  They simply waste memory.

That's the weird thing. For 24 bit mode, the X1000 AIC wants data in a 32-bit container, and if I recall correctly, even the I2S output is padded with zeroes out to 32 bits. So it's not like they're saving memory, as far as I can tell. And yeah, the PCM5102a dac accepts 32-bit data, though what it does internally I don't know.

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Audio Playback, Database and Playlists / Re: Bit depth, Dithering, and the Rockbox audio path

« Last post by saratoga on Today at 05:02:25 PM »

This is entirely out of pure curiosity, but I recently learned what dithering is, and noticed Rockbox has this capability. That got me thinking, I know parts of the RB audio path/pipeline are fixed to 16-bit. What does the audio path's bit depth look like, anyway? Maybe there's already a thread that explains this, but I did a quick search and didn't get much, especially within the last decade.

Say I've got a 32-bit FLAC file. I understand most of the sound processing stuff is 32-bit, so does it stay 32-bit all the way through the DSP stuff and then get truncated/dithered once to 16-bit, or does it get converted to 16-bit, upped to 32-bit (if stuff is enabled), and then converted again to 16-bit?

I don't think 32 bit flac exists, but ignoring that, since these are 32 bit processors without floating point everything is done natively on 32 bit.  At the end of processing it is converted to 16 bit in order to double the PCB buffer capacity and because most hardware expects 16 bit samples.  For the most part smaller than 32 bit samples are not used because they're slower on most of our hardware.

Another quite a bit more specific question... is dithering twice a bad thing, if the audio must be converted to lower bit depth twice? I'm working on getting higher bit depth volume working on the Eros Q, and it will go 16 --> 32 --> 24 (that's the plan, anyway...), could/should it be dithered there as well? Once I get the basic functionality working, anyway.

You only dither when reducing bit depth, never increasing.  In this case though its not needed since nothing can actually decode a 24 bit sample, so the dither would be lost anyway.

For reasons only Ingenic know, they limited the audio module in the X1000 processor to 24-bit samples, so that's the highest bit depth we can send to the DAC. Not bad by any means, but just like... why not 32?

Most real world hardware has somewhere between 14 to 18 bits, so values larger than 24 bit do not make sense.  They simply waste memory. 

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Audio Playback, Database and Playlists / Re: Bit depth, Dithering, and the Rockbox audio path

« Last post by dconrad on Today at 12:39:08 PM »

In your example, why go down to 24 bit again?

For reasons only Ingenic know, they limited the audio module in the X1000 processor to 24-bit samples, so that's the highest bit depth we can send to the DAC. Not bad by any means, but just like... why not 32?

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Audio Playback, Database and Playlists / Re: Bit depth, Dithering, and the Rockbox audio path

« Last post by 7o9 on Today at 12:26:08 PM »

I am not a mathematician so I googled.

Reading this explained to me what you are trying to decide: https://www.waves.com/audio-dithering-what-you-need-to-know

Quantization from higher bit depth to lower does not require dithering as a rule. Doing it multiple times adds noice each time. If you go up from 16/24 to 32 you are not losing any information. Changing the volume at 32 and then going back to the original should still bot lose information. Going from a 24 original to 16 does, as you have to perform quantization: https://en.wikipedia.org/wiki/Quantization_(signal_processing).

In your example, why go down to 24 bit again?

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Audio Playback, Database and Playlists / Bit depth, Dithering, and the Rockbox audio path

« Last post by dconrad on Today at 11:57:25 AM »

This is entirely out of pure curiosity, but I recently learned what dithering is, and noticed Rockbox has this capability. That got me thinking, I know parts of the RB audio path/pipeline are fixed to 16-bit. What does the audio path's bit depth look like, anyway? Maybe there's already a thread that explains this, but I did a quick search and didn't get much, especially within the last decade.

Say I've got a 32-bit FLAC file. I understand most of the sound processing stuff is 32-bit, so does it stay 32-bit all the way through the DSP stuff and then get truncated/dithered once to 16-bit, or does it get converted to 16-bit, upped to 32-bit (if stuff is enabled), and then converted again to 16-bit?

If the latter, is dithering applied both times the audio is converted down?

Another quite a bit more specific question... is dithering twice a bad thing, if the audio must be converted to lower bit depth twice? I'm working on getting higher bit depth volume working on the Eros Q, and it will go 16 --> 32 --> 24 (that's the plan, anyway...), could/should it be dithered there as well? Once I get the basic functionality working, anyway.

Edit: Or, really the ideal case would probably be to do volume scaling direct to 24 and avoid that whole question anyway, but I'd have to understand the math well enough to make that happen  One step at a time...

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Rockbox Utility / Re: iPod Classic 6g - bootloader not installing / storage issues

« Last post by millsy on July 21, 2021, 08:03:23 PM »

The 127G Partition is a limit set by the ipod official bootloader. I have this ipod working with a 256G iFlash drive. It is recommended you restore the ipod using iTunes rather than trying to format the disk yourself.

1. Plug iPod in normally
2. Restore iPod drive using iTunes
3. Ensure iPod restores to the "Choose a Language" screen
4. Close iTunes completely
5. Launch Rockbox Utility and proceed to install bootloader (only)
6. When requested, hold the reset [MENU+HOME] until notified of DFU mode (in 5 seconds, reboot starts, in 15 seconds, dfu mode starts, hold longer, reboot restarts)
7. Wait for Rockbox to restart. This sometimes fails, and requires a manual reset

If all goes well, your drive will still list 127G, but Disk Management software will see the additional partition space, and the iPod will show a black screen with some RockBox debugger information. Here's where it gets tricky. IF you resize the partition to fill the space, you'll lose the dual-boot mode. The iPod Classic 6th Gen will NOT boot properly if the partition is larger than the 127G, OR if any partition data exists outside of the 127G. Meaning using the space will require you to exclusively use RockBox. Once you've confirmed the desired partition table and formatted accordingly, you can proceed to use the Rockbox utility to install the firmware.

As an update on this, I found that this absolutely worked, though resizing didn't work I had to just delete all partitions and create a new fat32 one. I also found I had to assign it a drive letter manually (used AOMEI)

Seems the root cause of my issue was doing this in a VM, once I did it on native hardware I had no further issues!

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Audio Playback, Database and Playlists / Re: Making playlists on Desktop Win 10 is very difficult, what's the easiest way?

« Last post by JimR on July 21, 2021, 06:28:27 PM »

nrh93, I usePC3, a dedicated playlist creator. You need to adjust the path from, eg D:\music to /<microSD1>/music

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Rockbox General Discussion / Re: Will Rockbox ever be available for Sony NW-A55l?

« Last post by Loofer on July 21, 2021, 07:15:50 AM »

Just bumping this in the desperate hope that something has changed in the last 7 months? having lived with this thing I'd love to be able to get Rockbox functionality on it as the Sony software is driving me nuts at times.

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New Ports / Re: Fiio M3k

« Last post by amachronic on July 20, 2021, 05:50:36 PM »

while if i transfer files by connecting the fiio player via usb, compare the error message: insert a disk in the 'usb drive

It sounds like the problem is definitely due to USB handling in Rockbox. Just to confirm, does USB file transfer work correctly under the original FiiO firmware?

The error message you're getting is a bit suspicious. I can't say for certain but you may be hitting a known issue where the USB connection is detected but doesn't finish setting up properly. I don't know the cause of this problem so I can't say if/when it will be fixed... sorry.

As a workaround, you can always boot into the original firmware to use USB, or just use an external card reader.