Switch headphone source between input and DAC

Round down to 0 to avoid the buzzing noise issue

Fix phase modulation

AudioPlaySdWav Feature: togglePlayPause

AsyncAudioInputSPDIF3 minor bug fix/clipping prevention

sg5k: calcBiquad: add missing break; for hishelf

Add Teensy LC Code for PT8211

Add SGTl5000 MasterMode

Teensy LC AudioOutputI2S(+slave)

Fixes for Teensy LC

Fix documentation for SGTL lineInLevel (swap channels)

Update index.html

Band limited waveforms

MQS: Play nice

keeps 352kHZ PWM, but reduces hardware-oversampling to 32x

changed
{"type":"AudioOutputPWM",        "resource":"DAC1",           "shareable":false},
to
{"type":"AudioOutputPWM",        "resource":"PWM",           "shareable":false},

Attention this last part is *untested*

TBD: input as "Master". Do we need this?

Change delay(5) to delay(25)

Slavemode tested,
TODO: Test Mastermode (PCCM1802?)
TODO: Input

This adds a new enable() function.

bool enable(extMCLK, pllFreq);
switches the SGTL to Master Mode.

On LC this done automatically, so the normal enable() works with the Teensy LC.

Needed for Blocksize=128.
Blocksize 128 is needed for the waveplayer

There was a missing `break;` at the end of the FILTER_HISHELF
case in the calculations, meaning a hishelf coeff calc always
returned the default fallthrough case, which is a benign passthrough
filter.

Fix by adding the `break;`.

Fixes: #343

Signed-off-by: Graham Whaley <graham.whaley@gmail.com>

PT8211: fix beep on startup

https://forum.pjrc.com/threads/64592-Teensyduino-1-54-Beta-5?p=263595&viewfull=1#post263595

wav2sketch - Update for T4.x

Update effect_rectifier.cpp

Bug: was overwriting a read-only buffer

Minor gui text updates

Replace the text formula with a png graphic generated from some
LaTeX source.
Formulas in HTML apparently never made it in the mainstream,
and the recommendation is to use LaTex to generate images. See:
https://www.w3.org/MarkUp/HTMLPlus/htmlplus_45.html

To convert the .tex to a png, try:
  pdflatex formulas.tex
  convert -density 300 formulas.pdf -quality 95 formulas.png

Signed-off-by: Graham Whaley <graham.whaley@gmail.com>

Note in the GUI help text that the ToneDetect uses the
Goertzel algorithm.

Signed-off-by: Graham Whaley <graham.whaley@gmail.com>