README.md

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 LDAC Bluetooth earphones and DAC's under $30 (probably) especially when replaying 48 kHz tracks up-sampled over or equal to 96 kHz & 24 or 32 bits by AudioFlinger except the quality of internal speakers and a 3.5 mm jack receiving 48 kHz audio data without re-sampling 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.

By the way, although most people might wonder how this module improve the audio quality of such devices, it is accomplished by very long filter length re-sampling near ideally (almost without pre-echo, ringing (post-echo) and aliasing noise) cutting off a frequency zone from just above 20 kHz filled with ultrasonic noise (although most people believe part of natural sound) generated by high frequency dithering (also called delta-sigma modulation, noise-shaping, super bit-mapping, etc.) at recording time and even 16 bits noise-shaping rounding output time (e.g., Opus decoders), and deteriorating audible sound like a thin veiling smokescreen by intermodulation significantly amplified by large amplification non-linearity of LDAC Bluetooth earphones and DAC's under $30. Furthermore this can be considered to be a kind of decimation filtering from 48 kHz & 16 bits samples (having dynamic range larger than usual 16 bits limit with ultrasonic noise) 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 LDAC Bluetooth earphones (any devices, as far as I know) and DAC's under $30 (typically using DAC chip CX31993, ALC5686, KT0210, etc.).

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 together or not.

Notes:

• If you feel your LDAC earphones or "cheapie" DAC wouldn't become to sound good at all, try editting "service.sh" script in the installed place or its ZIP archive so as to replace "83" in it with "84" or "85" for appropriately cutting off ultrasonic noise causing intermodulation.
• This module doesn't have the effect for Hires. tracks (greater than 48 kHz sample rate) which not having large pre-echo and ringing, and high frequency dithering noise, except ultrasonic noise added on purpose for mellowness. Anyhow, if you want to improve the quality of only Hires. tracks on "cheapie" devices, edit "service.sh" script in the installed place or its ZIP archive as described in the script.
• LDAC earphones and 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 post re-sampling (48 kHz to 96 kHz) and it is so much worse than this re-sampling.
• Also don't forget disabling "Absolute Volume" of Bluetooth devices in developer settings and setting a volume at the device side to be maximum for the best audio quality by avoiding analog low-pass filtering on portable devices having very large input parasitic capacitance.

• 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
  194	520		98	Ultra Hi-Fi for audio devices having small amp. non-linearity
  Parameters of this module:	-	-	-	-
  194	520	91 ~ 94		AAC or Flac 44.1kHz; for LDAC BT earphones and DAC's under $30 both having large amp. non-linearity
  194	520	83 ~ 86		Opus 48kHz; for LDAC BT earphones and DAC's under $30 both having large amp. non-linearity
  194	520	42,43		Hires. 96kHz; for LDAC BT earphones and DAC's under $30 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	ES9038PRO (Fast roll-off N-fold over-sampling)
  vary 50 ~ 118	34	96	(398)	ES9039PRO (Fast roll-off N-fold over-sampling)
  110	40	(96)	109	CS43131 (Fast roll-off N-fold over-sampling)
  110	40	(96)	109	CS43198 (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)

  • % in "Cut-off" and "Stop band" (starting from) fields means the proportion to the Nyquist frequency.
    

• 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	ES9039PRO Fast roll-off
  Mastering tool	slight	slight	light	iZotope, No Alias (guess)
  Audio misc. settings	almost none	almost none	light	Ultra Hi-Fi
  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 LDAC BT earphones and DAC's under $30

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.