yzyhk904 / resampling-for-cheapies

Setting re-sampling parameters of AudioFlinger (the system-wide mixer) so as to improve audio quality of DAC's under $30 and LDAC BT devices especially

This repository has been moved to "Magisk-Modules-Alt-Repo".

A Magisk module resampling for cheapies

This module has been developed for casual users to overide re-sampling parameters of AudioFlinger (the system-wide mixer) in my other modules ("Audio misc. settings" and "Hifi Maximizer") so as to significantly improve audio quality of DAC's under $30 (probably) and LDAC bluetooth devices especially when replaying 44.1 kHz tracks up-sampled over or equal to 96 kHz & 24 bits by AudioFlinger, but also the quality of internal speakers and a 3.5 mm jack receiving 48 kHz & 24 bits audio data (except 48 kHz & 16 bits) up-sampled by AudioFlinger. If you are an audiophile expert, please use "extras/change-resampling-quality.sh" in "USB SampleRate Changer" which can change the parameters on the fly flexibly.

And its effect is accomplished almost without pre-echo, ringing (post-echo) and aliasing noise by very long filter length re-sampling near ideally cutting off a frequency zone from just above 20 kHz filled with ultrasonic noise generated by high frequency dithering and deteriorating audible sound by intermodulation significantly amplified by large amplification non-linearity of DAC's under $30 and LDAC BT devices. Furthermore this can be considered to be a kind of decimation filtering from 44.1 kHz & 16 bits samples to 40 kHz & 24 or 32 bits ones except the ultrasonic noise by hight frequency dithering. So it has little effect when using AAC and SBC codecs which transmit audio data by 44.1 kHz & 16 bits.

However, as the noise has a merit adding mellowness into audible sound in the case of none cheap DAC's having very small amplification non-linearity, please use this module only when using DAC's under $30 (probably) and LDAC bluetooth devices.

Finally, this module is designed to override re-sampling parameters set by my other modules, but can be used by itself only. You can install this module and enjoy its effect whether you are using one of them or not.

Notes:

• This module doesn't have the effect for HIRES. tracks (greater than 44.1 kHz sample rate) which not having large pre-echo and ringing, and high frequency dithering noise.
• DAC's deteriorate the quality more or less by their internal over-sampling filtering when receiving low sample rate data.
• Don't forget disabling "A2DP hardware offload" on Snapdragon devices (if you can), because it forces double re-sampling (44.1 kHz to 48 kHz, and 48 kHz to 96 kHz) and it is so much worse that the latter re-sampling guts the former one at all.

• Appendix A. Examples of Re-sampling Parameters :

  Stop band attenuation (dB)	Half filter length	Cut-off (%)	Stop band (%)	Memo
  AOSP parameters:	-	-	-	-
  90	32	100		Default Quality
  80	16	100		LOW Quality
  84	16	100		MED Quality
  98	32	100		HIGH Quality
  Parameters of Audio misc. settings:	-	-	-	-
  159	480	92		Old devices of A11 and earlier
  165	360		104	Low performance devices of A12 and later with audio ones having small amp. non-linearity
  179	408		99	General purpose on A12 and later for audio devices having small amp. non-linearity
  Parameters of this module:	-	-	-	-
  179	520	94		for DAC's under $30 and LDAC BT devices both having large amp. non-linearity
  External examples:	-	-	-	-
  100	29	(91)	109	AK4493 (Sharp roll-off N-fold over-sampling)
  150	42	(91)	109	AK4191EQ (Sharp roll-off N-fold over-sampling)
  120	35	(97)	110	ESS 9038PRO (Fast roll-off N-fold over-sampling)
  50 ~ 118	34	96	(398)	ESS 9039PRO (Fast roll-off N-fold over-sampling)
  110	40	(96)	109	CX43131 (Fast roll-off N-fold over-sampling)
  98	130	98.5		MacOS Leopard (guess)
  159	240		99	iZotope, No-Alias (guess)
  100	64		99	SoX HQ linear phase (guess)
  170	520		99	SoX VHQ linear phase (guess)

• Appendix B. Characteristics of Re-sampling Parameters :

  Category	Background opaqueness (aliasing noise)	Pre-echo and ringing	Mellowness (intermodulation)	Memo
  DAC	light	heavy	heavy	AK4491EQ Sharp roll-off
  DAC	medium	medium	light	ESS9039PRO Fast roll-off
  Mastering tool	slight	slight	light	iZotope, No Alias (guess)
  Audio misc. settings	almost none	almost none	light	for general purpose
  Audio misc. settings	very slight	very slight	medium	for low performance devices
  Audio misc. settings	slight	almost none	almost none	for old devices
  This module	almost none	almost none	very slight	for DAC's under $30 and LDAC BT devices

DISCLAIMER

• I am not responsible for any damage that may occur to your device, so it is your own choice whether to attempt this module or not.