Discussion about a simple way to change the sample-rate

[Tibbar]

Hi,

I just tried the code out in message #44 and received the following error message when. compiling.

'clkArr' was not declared in this scope

Any ideas?

Thanks!

[defragster]

Looking at the code its definition is based on the value of the F_PLL.

What Teensy and clock speed is in use?

Write a short sketch using the same compile params and speed and Serial.print( F_PLL ) and Serial.print( F_CPU )

[Tibbar]

Thanks for replying so quick!

I'm using T3.5 running at 168MHz. I just changed it to 120MHz and it compiled OK!!

[ahinduja]

Hi Frank,
I wanted to tryout your sample rate changing code for the Teensy 4, which I pulled from CorBee's Bat Detector repo on github. It seems that it's not perhaps compatible with the Teensy 4 as I2S0_MCR & I2S_MCR_DUF are showing up as undefined during compilation. On a more recent thread Paul mentioned that the 3.6 and 4 have different ways of using the MCLK as seen here. What changes should be needed for the Teensy 4? Any resources I should look into?
Thanks
-Akshay

[Jaco Versfeld]

Good day,

I encounter the same issue as mentioned in the last post. How can we adapt the code for the Teensy 4.1?

Thank you,
Jaco

[Gambalunga]

Hi all

This is my first post on this forum and it touches on a subject that I am having difficulty getting my head around. I know this thread is now somewhat ancient history but it turned up when I was searching for a way of resolving my particular problem

Unlike some I am not interested in a high audio sample rate but in a relatively low one. The reason is that I want to play a simple WAV file that has been stored on the flash memory of an Adafruit Feather M4 Express. The 2MB of space available allows the storage of about 2 minutes an 8 bit mono audio with sample rate of 16000 Hz. I wish to play this over one of the internal DACs on the SAMD51.

I have used an updated version of the SamdAudio library to get it working on Feather M0 Express ( https://github.com/Gambalunga/Audio_FeatherM0 ) but that will not compile for the M4.

I have tried using the Adafruit fork of the Teensy Audio library and managed to get the example sketch WavFilePlayer.ino (with a tiny mod) to compile and load. Clearly, however, 2MB of on board flash is not going give any useful period of sound at stereo 44117 Hz. and I can get it playing about 11 seconds of music.

I noted the section of code below but I am not sure if it is relevant to my problem or even how to implement it in the sketch.

Here's the same for the internal DACs :

void setDACFreq(int freq) {
const unsigned config = PDB_SC_TRGSEL(15) | PDB_SC_PDBEN | PDB_SC_CONT | PDB_SC_PDBIE | PDB_SC_DMAEN;
    PDB0_SC = 0;
    PDB0_IDLY = 1;
    PDB0_MOD = round((float)F_BUS / freq ) - 1;    
    PDB0_SC = config | PDB_SC_LDOK;
    PDB0_SC = config | PDB_SC_SWTRIG;
    PDB0_CH0C1 = 0x0101;    
}

edit: Added one line

I noticed the following section of code in AudioStream.h and wondered if it could be modified to give me the 16000 sample rate that I require.

#ifndef AUDIO_SAMPLE_RATE_EXACT
#if defined(__MK20DX128__) || defined(__MK20DX256__) || defined(__MK64FX512__) || defined(__MK66FX1M0__)
#define AUDIO_SAMPLE_RATE_EXACT 44117.64706 // 48 MHz / 1088, or 96 MHz * 2 / 17 / 256
#elif defined(__MKL26Z64__)
#define AUDIO_SAMPLE_RATE_EXACT 22058.82353 // 48 MHz / 2176, or 96 MHz * 1 / 17 / 256
#elif defined(__SAMD51__)

//#define AUDIO_CLKRATE (SystemCoreClock >> 6)
//#define AUDIO_PRESCALER TC_CTRLA_PRESCALER_DIV64
//#define AUDIO_SAMPLE_RATE_EXACT 22058.82353 // 120 MHz / 64 / 85 
//#define AUDIO_TC_FREQ 22000

#define AUDIO_CLKRATE (VARIANT_GCLK2_FREQ >> 4)
#define AUDIO_PRESCALER TC_CTRLA_PRESCALER_DIV16
#define AUDIO_SAMPLE_RATE_EXACT 44014.085 // 100 MHz / 16 / 142
#define AUDIO_TC_FREQ 44100

#endif // SAMD51
#endif // AUDIO_SAMPLE_RATE_EXACT

It seems to me that if the following were defined with different values I may be able to get the 16000 Hz that I require:

AUDIO_CLKRATE (VARIANT_GCLK2_FREQ >> 4)
AUDIO_PRESCALER TC_CTRLA_PRESCALER_DIV16
AUDIO_SAMPLE_RATE_EXACT 44014.085 // 100 MHz / 16 / 142
AUDIO_TC_FREQ 44100

Does anyone have any idea of how this may be made to function?

perhaps defining
AUDIO_SAMPLE_RATE_EXACT 16025.641 // 100 MHz / 16 / 390
and
AUDIO_TC_FREQ 16000

It seems too easy and I am not sure if that "390" has to be specified somewhere else or even if it can be used.

[PaulStoffregen]

This forum is for Teensy. If you're using Adafruit's hardware (and their modified copies of Teensy's software), ask for support on Adafruit's forum.

[alfa66]

@FrankB, I am having a hard time understanding how to change the sampling frequency of the PT8211 using your routines...
When I try to use your routines I2S_MDR_DIVIDE and I2S_MDR_FRACT are not defined.
These are my #include
#include <Arduino.h>
#include <Audio.h>
#include <AudioStream.h>
#include <DMAChannel.h>
What am I missing?
Thank you so much!

[Frank B]

On a Teensy4?
Try this:

#include <utility/imxrt_hw.h> 


void setI2SFreq(int freq) { //Teensy 4
  // PLL between 27*24 = 648MHz und 54*24=1296MHz
  int n1 = 4; //SAI prescaler 4 => (n1*n2) = multiple of 4
  int n2 = 1 + (24000000 * 27) / (freq * 256 * n1);
  double C = ((double)freq * 256 * n1 * n2) / 24000000;
  int c0 = C;
  int c2 = 10000;
  int c1 = C * c2 - (c0 * c2);
  set_audioClock(c0, c1, c2, true);
  CCM_CS1CDR = (CCM_CS1CDR & ~(CCM_CS1CDR_SAI1_CLK_PRED_MASK | CCM_CS1CDR_SAI1_CLK_PODF_MASK))
       | CCM_CS1CDR_SAI1_CLK_PRED(n1-1) // &0x07
       | CCM_CS1CDR_SAI1_CLK_PODF(n2-1); // &0x3f 
}

[alfa66]

Thank you for all your great contributions to the Forum, @frankB

[M4ngu]

This works pretty good! thanks Frank B,
I'm getting some issues with abrupt changes to lower values, sound turns off if I switch from 44100 to 22050, but it works fine with other values ...and I have no idea why,

45100 -> 22550 ok
44100 -> 22050 no sound
43100 -> 21550 ok

[Frank B]

I don't know, why. Maybe try to disable the interrupts when switching the rate. I have never tried that - But I know of an application that sets 176khZ in one step, without problems.

[M4ngu]

I don't know, why. Maybe try to disable the interrupts when switching the rate. I have never tried that - But I know of an application that sets 176khZ in one step, without problems.

that's the first thing I tried, with no luck. Indeed I can change the frequency from 44100 to 88200 with no problem, the 'no sound' issue occurs when jumping below 44100, anyway what I did is to disable 1 octave changes below 44k1,