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I suggest to block all 'hate' speech on this forum

com'on, there are multiple posts and threads about this!

You can easily ignore lack of USB connection
Yes, it fills-up a buffer, but when this buffer is full all further data are dropped.
You can see that by writing data to USB, disconnecting USB from PC...

the constant is a float (single and not double)

see post #2
now you have to remove the -6.0f
(6db is equivalent to a amplitude factor of 2)

because of factor 2

You always can use SDIO protocol (even if nobody has done so far AFAIK)

This is partially done in Serial, but I agree that checking for open session is a good idea, especially as PC will time out MTP when session is not established for some time (have not established...

In MTP I'm using

extern volatile uint8_t usb_configuration;
to know if usb is configured (taken from other devices)
it is 0 when not initialized

I'm afraid that I have no experience with midi, but I can tell you that the 2nd usb was modelled after T4 so T4 midi would be a good starting point.

But if you wanted to take on the challenge, I...

https://github.com/WMXZ-EU/USB2
I did it for T3.6 but have not ported this functionality to T4
(too busy with priority job)

can or must?

which teensyduino?

have a look onto schematic: VBAT-pin and 3.3V are combined with diodes to go to Teensy

I tend to disagree
what-ever system is pre-loaded, you will find people that complain or want something else.

I like the idea of having only the blink preloaded to prove functionality of a new...

I only wanted to clarify the "d - first dump list of storages" option
this prints out the relevant info of the index file, mtp uses to access the files.
It is only useful during development and...

One application of MTP is to transfer files, while the Teensy is not accessible, so disk access should IMO be optimised.
If this can be done using info from filesystem, so better. Yes, FS.h should...

Well, I only adapted the original code to my needs and made it available.
I understand that Paul is interested to integrate it at some time, but he seems to be busy with other (hopefully pleasant)...

The 2.9 ms is result of acquisition buffer (128 samples) and sampling rate (44.1 kHz) so you must change one of the two values to change the delay.
This requires changing some basic parameters. It...

They cannot be 180 deg out of phase. there is a fixed travel time through the audio library
Output is NEVER without delay to input.

AFAIK
I2S-input: data are buffered for 128 samples (2.9 ms...

the way it is wired now, connect audio signal to both line in and oscilloscope channel 1 to ,say, left and channel 2 to right
you could simplify, by connecting both amp inputs to same i2s input...

sorry about formating
here is the audio code

#include <Audio.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <SerialFlash.h>

// GUItool: begin automatically generated code

no, I was suggesting
i2s ->mixer (+1) -> I2S left
|-> mixer (-1) -> I2S right
so left and right path have same internal delays

if you insert an audio object then you have to consider a 128 sample delay.
So, insert two mixers in parallel one with +1 and the other with -1, then you should get the desired effect

the SPI speed and the CPU speed are total different clocks
.
However, if you use code where SPI clock speed is derived from CPU clock then you may run into issues.
If this happens in old low...

use
SPI1.beginTransaction(SPISettings(4'000'000, MSBFIRST, SPI_MODE0));

spi commands

SPI1.endTransaction();

or similar to control SPI speed (here 4 MHz)

which library you are using?
could not find a MPU9250 for SPI that is compatible with your code

I use 5 lines into my waterproof housing
Voltage, Ground, USB D+, USB D-, Program line
this allows me to reprogram Teensy at all circumstances.

Yes but SE
A10,A11 are Differential (it is clearly written)

I corrected the Readme file (thanks for pointing out)

re TyCommander, I'm not using this, so I cannot comment
If you update boards.txt (modifications for teensy_avr) then there should be two...

USB mode is fixed at compile time.
You can use MTP with Serial if you install MTP from https://github.com/WMXZ-EU/MTP_t4 and follow instructions

I had that too, but having storageID above 16 bit did not change anything.
I know it violates the document, but coding was simpler.

one events:
notifying every new file, for me is not an option,...

maybe one needs an ISR also for events. don't think TX ISR is called.

@KurtE
On T3.x, my interpretation was that after malloc you need also a free, but I may be wrong.
So I use always the same buffer for multiple events, assuming that I will not send multiple events...

BTW,
My Github has also a tested T3.6 version on events included (in MTP.cpp)
I would keep event handling outside cores
I did a couple of days ago a PR on teensy3/usb_desc.h to have tx events,...

MTP per se does not need Serial connection, but MTP is usually integrated in other programs that need serial connections.

Seremu without Arduino monitor is a little bit complicated.
Consider...

@KurtE,
Yes I'm following your modifications and try them out.
There are couple of things I may have a different starting point, so I'm curious to see how they work out.
So please go ahead with...

That is my observation also.
F5 seems to be necessary

and 3 characters after the "."

Teensy4.x are 3.3V I/O so do do not want a board that is made to interface with a 5V board.
5V in Teensy4 pins may kill these pins

what about

extmem_malloc(size)
as used in LittleFS_RAM of LittleFS library?

Chip,
mtp-test.ino does work now with T3.6
to use USB_MTPDISK_SERIAL you need to copy the desc.h parts into desc.h cores files
if you prefer to use old mtpdisk (seremu) you should edit desc.h to...

Chip,
Have not integrated yet events to T3.6.
I'm still testing with T4.1 (my real application runs on T4.1)
T3.6 needs own usb interface so it needs a mind-change to get integrated.
otherwise it...

Chip
you mean
N_k = (Q * f_s) /f_k

anyhow, it does not matter, as one can use FFT to approximate the spectral resolution (with summing of bins), then one can sum the temporal bins to...

AFAIK
N_k * f_k = Q*f_s

N_k window length
f_k center frequency
f_s sampling frequency

see e.g. https://en.wikipedia.org/wiki/Constant-Q_transform
Obviously, one needs to read a little bit...

Chip,
I would not call it "approximation to constant-Q", as a simple logarithmic frequency scale (logarithmic summing frequency bins) is equivalent to a logarithmic Q.
In how far logarithmic...

The OP and title asks about constant Q and not "logarithmic" spectrograms.
constant Q indicates "logarithmic" spacing of frequencies AND therefore also logarithmic changes in window size.
summing...

As Q is related to the time-frequency product you "only" need to implement 96 DFTs, each with own window size.
Edit: Not sure is there is a DFT object in Audio library, but you can easily write one...

@KurtE
Re storageID, I knew this and have thought to separate physical and logical storage, but in the end I let everything as 1 physical storage (0<<16) and consider all storage as logical. I know...

After commenting to @mborgerson, here a first success
I succeeded to provoke a PC response using an event.
Using a device reset event PC reopened a new session. I updated the MTP github.
in MTP.h...