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TransPCM—use Float16/24 to reduce bit-depth, also promotes compression, 2013-05-30: beta 0.1.3a / formerly HalfPrecision / ref.: IEEE 754-2008
Nick.C
post Sep 12 2011, 22:03
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When I first became aware of the Float16 type I found it interesting in terms of maybe having potential as a possible lossy storage type.

Attached is a processed version of the sample in this thread which has been decoded back to PCM. The processing is as follows (at this stage as there is no player that I am aware of):
Input file Sample [PCM] > FLOAT16 > [PCM] > Output File.

The conversion from integer to Float16 reduces the number of significant bits of the 24-bit sample to (a maximum of) 11. There is therefore an amount of added noise due to truncation. The added noise has been noise shaped using SG's adaptive noise shaping method as used in lossyWAV.

Original Sample

Lossy Float16 Processed Sample [edit] removed due to TransPCM executable / foobar2000 Float16 playback availability, 29th May 2012. [/edit]

If the 24-bit coded sample is encoded with FLAC (wFormatTag left as 0x0001 as FLAC does not handle Floating Point samples and wBitsPerSample is left as 24) there is a saving of in excess of 20% in filesize.

I don't see any practical advantage using this storage type for native 16-bit PCM.

Changelog:

TransPCM beta 0.1.3a 30/05/2013
  • Bug fix in Float24 handling (thanks Bryant!).
  • Bug fix in WAVE_FORMAT_EXTENSIBLE chunk handling (thanks again Bryant!).
TransPCM beta 0.1.2 02/06/2012
  • Modification to adaptive noise shaping for 44.1/48kHz input;
  • Amendment to tracer fingerprinting.


This post has been edited by Nick.C: May 30 2013, 07:57
Attached File(s)
Attached File  TransPCM_beta_0.1.3a.zip ( 79.66K ) Number of downloads: 81
 


--------------------
lossyWAV -q X -a 4 --feedback 4| FLAC -8 ~= 320kbps
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Nick.C
post Dec 23 2011, 08:20
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.... a surprise, yes, however as the standard has not become widespread in terms of implementation then I think that Float16 being different is understandable / acceptable in the same way that 8-bit integer is unsigned with a 128 offset compare to 16/24/32 bit signed integers with no offset.

[edit] In terms of headroom, due to the added noise associated mantissa bit reduction, I would expect Float16 to be a final format rather than an interim step for further processing. Use of the full range available in Float16 was a very conscious decision to maximise range (min sample value to max sample value). Also, there is nothing stopping someone reducing the scale of the audio prior to converting to Float16. [/edit]

In my testing, Float16 in a 24-bit sample container compressed better than the same number of 24-bit integer samples upon which the Float16 samples were based. Unfortunately, now that HalfPrecision stores the FMT.wFormatTag properly (0x0003 for Float), FLAC will not compress Float16 output.

HalfPrecision beta 0.1.0b attached. [edit3] superseded, 29th May 2012 [/edit]
  • Correction files implemented;
  • CRC32 and CRC16 calculated and stored for audio data to allow checking of successful recombination;
  • Code speedups.


[edit2] experimental Adaptive Noise Shaping coefficients snuck through.... beta 0.1.0b replaced. [/edit2]



This post has been edited by Nick.C: May 29 2012, 21:37


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lossyWAV -q X -a 4 --feedback 4| FLAC -8 ~= 320kbps
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Gumboot
post Dec 23 2011, 08:43
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Well, by "huge surprise" I mean "destroy your speakers", and by "any software" I mean that I have to contact my previous employer and have them check to see if I committed that code before one of these files gets into a mobile phone and is played at high volume through a set of earbuds.


QUOTE
In terms of headroom, due to the added noise associated mantissa bit reduction, I would expect Float16 to be a final format rather than an interim step for further processing.


This raises the question of why you need so much low-level resolution, then.
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Posts in this topic
- Nick.C   TransPCM—use Float16/24 to reduce bit-depth, also promotes compression   Sep 12 2011, 22:03
- - AndyH-ha   This differs from simply reducing the bit depth?   Sep 12 2011, 22:11
- - Nick.C   Yes - in that values up to c. +/- 2^31 can still b...   Sep 12 2011, 22:19
- - saratoga   Isn't this pretty much what ADPCM does? Excep...   Sep 12 2011, 22:32
|- - C.R.Helmrich   You mean a-Law/µ-Law? Makes me wonder how many bi...   Sep 12 2011, 23:05
- - bryant   QUOTE (Nick.C @ Sep 12 2011, 14:03) Attac...   Sep 13 2011, 06:13
- - Nick.C   The plan was to simply set wFormatTag= 0x0003 and ...   Sep 15 2011, 21:09
|- - benski   QUOTE (Nick.C @ Sep 15 2011, 16:09) The p...   Sep 16 2011, 14:03
- - knutinh   float16 could be very efficient on GPU hardware if...   Sep 16 2011, 13:49
- - Nick.C   I understand that currently players are rather unl...   Sep 16 2011, 19:26
- - Nick.C   Below is Delphi / IA32 & x87 code used to enco...   Sep 22 2011, 13:05
- - Nick.C   HalfPrecision beta 0.0.2cd attached. [bugfix] [sup...   Oct 20 2011, 12:53
|- - Gumboot   QUOTE (Nick.C @ Oct 20 2011, 11:53) NB: t...   Dec 22 2011, 23:19
- - lvqcl   foobar2000 1.1.9 beta1: "Implemented experime...   Oct 22 2011, 10:54
- - Nick.C   RE: TransPCM—use Float16/24 to reduce bit-depth, also promotes compression   Oct 22 2011, 14:24
- - Nick.C   HalfPrecision beta 0.0.2e attached [superseded]. F...   Oct 24 2011, 18:23
- - pdq   I once had an idea for how to encode audio data. T...   Oct 24 2011, 19:29
- - Nick.C   That would be one way of doing it. However sample ...   Oct 24 2011, 21:02
- - Nick.C   HalfPrecision beta 0.0.2f attached superseded . ...   Nov 1 2011, 13:53
- - Nick.C   HalfPrecision beta 0.0.2g attached. Superseded. ...   Nov 10 2011, 13:41
- - Didjeridoo   Nick.C Thank you for your innovation. It remains t...   Nov 11 2011, 11:36
- - Nick.C   @Didjeridoo: Thanks - I am also looking forward to...   Nov 11 2011, 23:05
- - Nick.C   HalfPrecision beta 0.0.2h attached. Superseded ...   Nov 14 2011, 21:22
- - Didjeridoo   Nick.C I watch all the moves and develops Is not...   Nov 15 2011, 10:32
|- - lvqcl   QUOTE (Didjeridoo @ Nov 15 2011, 13:32) P...   Nov 15 2011, 15:53
- - Ljubo44   Do you have any sample of command line for foobar.   Nov 15 2011, 19:13
- - Nick.C   HalfPrecision beta 0.0.2i attached. Superseded. F...   Nov 15 2011, 20:05
- - Ljubo44   on 16/44,1 size is same after compress halfp.wav 1...   Nov 15 2011, 21:24
|- - Nick.C   QUOTE (Ljubo44 @ Nov 15 2011, 20:24) .......   Nov 15 2011, 22:05
- - Ljubo44   You are right, I used foobar 1.1.9 to convert to f...   Nov 15 2011, 22:37
- - Nick.C   HalfPrecision beta 0.0.2j attached. Superseded. ...   Nov 15 2011, 23:02
- - Nick.C   HalfPrecision beta 0.1.0a attached. Superseded. ...   Nov 17 2011, 14:20
- - Didjeridoo   I hope the developers do not ignore innovation   Nov 18 2011, 19:44
- - Nick.C   foobar2000 1.1.10 beta 1 adds Float24 support - re...   Nov 18 2011, 21:24
- - pompon   QUOTE (Nick.C @ Sep 12 2011, 16:03) When ...   Dec 5 2011, 06:37
- - FreaqyFrequency   @pompon: This is different from those coding sche...   Dec 5 2011, 08:44
- - Nick.C   Right then people - HalfPrecision needs a new name...   Dec 22 2011, 20:34
- - Nick.C   .... a surprise, yes, however as the standard has ...   Dec 23 2011, 08:20
|- - Gumboot   Well, by "huge surprise" I mean "de...   Dec 23 2011, 08:43
|- - Nick.C   It would surprise me if, when using any type of fl...   Dec 23 2011, 09:01
|- - Gumboot   Well it's not really in its infancy. I includ...   Dec 23 2011, 22:02
- - Nick.C   I accept that the Float16 proposal must have been ...   Dec 27 2011, 21:34
- - FreaqyFrequency   I fear that I may need a little more clarification...   Jan 9 2012, 05:48
- - Nick.C   Hi there, Using HalfPrecision to convert from 24-...   Jan 9 2012, 20:05
- - FreaqyFrequency   Thanks for the reply, Nick. Looking at the Replay...   Jan 10 2012, 03:36
- - Nick.C   TransPCM beta v0.1.1 attached. Superseded Chang...   May 29 2012, 21:51
- - Nick.C   TransPCM beta 0.1.2 attached. Superseded. Chang...   Jun 2 2012, 13:57
- - Ljubo44   CODE/d /c C:\bin\TransPCM_beta_0.1.2...   Jun 14 2012, 01:29
|- - lvqcl   QUOTE (Ljubo44 @ Jun 14 2012, 04:29) What...   Jun 14 2012, 15:47
- - db1989   Why do you have switches before the executable? An...   Jun 14 2012, 09:02
- - Nick.C   The use of --stdinname %d is to tell the program w...   Jun 14 2012, 17:47
- - Nick.C   Rockbox now has added Float16 compatibility* - tha...   Nov 24 2012, 23:15
- - saratoga   No problem. Hope its useful to people.   Nov 25 2012, 00:28
- - Nick.C   TransPCM beta 0.1.3a attached to post #1 in this t...   May 30 2013, 07:58


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