SD Audio playback speed

[Geroge]

Hello

Trying to find out if it is possible to play audio files from an sd card while adjusting the speed of which the audio files are played at. I would only need to change the speed by -10% / +10%. This seems like a bit of a grey area atm so any guidance would be greatly appreciated. I am using a teensy 3.6 with a teensy audio adapter.

Cheers!

[WMXZ]

Hello

Trying to find out if it is possible to play audio files from an sd card while adjusting the speed of which the audio files are played at. I would only need to change the speed by -10% / +10%. This seems like a bit of a grey area atm so any guidance would be greatly appreciated. I am using a teensy 3.6 with a teensy audio adapter.

Cheers!

Reading from SD card is independent from playing audio. As audio sampling rate is fixed, you could insert a resampling filter between sd card read and audio output. However, I do not know if there are examples available.

[Geroge]

Reading from SD card is independent from playing audio. As audio sampling rate is fixed, you could insert a resampling filter between sd card read and audio output. However, I do not know if there are examples available.

Hmmm massive over-sight on my behalf, should have noticed on that one. I am trying to make a small beatmatching tool, kind of based off cdj 500s. Forgive me as I am pretty new to this, but is there a way of slowing down / speeding up the sd card read rate? Doesn't exactly need to sound good. I noticed that with the flash memory chip installed on the audio board you can get about 8 sec of delay, perhaps this could be used for a re-sampling filter?
Cheers

[PaulStoffregen]

is there a way of slowing down / speeding up the sd card read rate? Doesn't exactly need to sound good.

So far nobody has written the code to do this. It's on my todo list, together with *many* other features. I do not have a solid timeframe for when I'll get around to it.

To specifically answer your "is there a way" question, yes, there most certainly is a way. But that way involves pretty substantial programming effort within the library. If "a way" is restricted to mean only ways that involve using existing audio library features without difficult programming, then no, there isn't currently such a way.

I noticed that with the flash memory chip installed on the audio board you can get about 8 sec of delay, perhaps this could be used for a re-sampling filter?

This is purely a matter of software. The extra memory chip is not needed and would not significantly help. In fact, the software would likely be much more difficult to write if it unnecessarily tried to use that chip in some way.

[Geroge]

Great this clears up a lot thank you. Looking forward to this feature being implemented, along with the many others!

Cheers!

[floretan]

I had an unsuccessful go at this a few months ago, the goal was to be able to detune samples for a sample-based keyboard.

Reading from SD card is independent from playing audio, but the code for AudioPlaySdRaw reads data from the SD card in chunks matching the audio buffer size. Reading at double or half speed is relatively easy, but something like 10% slower/faster would require keeping track of excess data that's already read but doesn't fill an entire audio buffer yet. My attempt just resulted in a lot of terrible noise with a hint of the original sound.

[Frank B]

I had an unsuccessful go at this a few months ago, the goal was to be able to detune samples for a sample-based keyboard.

Reading from SD card is independent from playing audio, but the code for AudioPlaySdRaw reads data from the SD card in chunks matching the audio buffer size. Reading at double or half speed is relatively easy, but something like 10% slower/faster would require keeping track of excess data that's already read but doesn't fill an entire audio buffer yet. My attempt just resulted in a lot of terrible noise with a hint of the original sound.

Have you tried to sync the speed-change with the audioblocks (speed-change only when between blocks)

[Moo]

I was also looking for some kind of playback speed control, and since I didn't find any solutions and quite a few people who seems to have a similar requirements, I thought I'd see if I could hack it... well at least the easy version, which is resampled RAW files...

I implemented a ResamplingSdReader class which has equivalent methods to File::read(char *buf, long len) but returns a resampled buffer instead of direct buffer from file.

I've copied play_sd_raw class to play_sd_raw_resampled class and added method setReadRate(float f): where 1 would be regular playback rate, 0.5 half speed, 2 double speed, etc). [Maybe it should be called setPlaybackRate?]

I've forked https://github.com/PaulStoffregen/Audio -> https://github.com/newdigate/Audio, added this feature, even tested briefly on a teensy, and to my surprise to seemed to work really nicely.

https://github.com/newdigate/Audio/c...47aecc0c7a1960

if anybody is interested, I'd be happy to send pull request to PaulStoffregen/Audio

A nice improvement would be to implement an option to enable linear interpolation on the resampled output.

It would also be nice to be able to play WAV files at arbitrary rates.

[Moo]

I moved the variable playback rate feature to its own branch here https://github.com/newdigate/Audio/t...-raw-resampled

I've briefly tested the code, seems to be okay between -1.0 and 1.0, posted quick video https://www.youtube.com/watch?v=rEEJf7q9tRY (apologies - its pretty raw)

If anybody has the time and inclination, I'd be interested to know your thoughts/experiences/questions...

Im planning on using this feature with a tempo synch'ed teensy audio recorder/looper... Also like to see if I can get it to work with .wav files

[bobkruijer]

This looks cool, I'll try this at some point. Were there any artefacts above 1.0 or -1.0 values as you have only tested that?

[Moo]

Subsequently I’ve tested it between -4.0 and 4.0... works successfully. beyond that I’ve not tested.

[propa]

Subsequently I’ve tested it between -4.0 and 4.0... works successfully. beyond that I’ve not tested.

Hi Moo,

Is there any reason your code only works with Teensy 3.6? Can't seem to get it to compile for 3.2 sadly. Will buy a 3.6, but wondering what the issue is with 3.2 compatibility.

Great work, can't wait to try it out. And sounds like wobbly glitch hop in the video, nice work!

[Moo]

Oh... I didn't realise it wasn't compiling for teensy 3.2 - Im sure it should be able to - I'll have a look when I get a moment, thanks for letting me know...

I got alot of satisfaction from turning that knob back and forth, it sounds just like an old vinyl being scratched....

[propa]

Oh... I didn't realise it wasn't compiling for teensy 3.2 - Im sure it should be able to - I'll have a look when I get a moment, thanks for letting me know...

I got alot of satisfaction from turning that knob back and forth, it sounds just like an old vinyl being scratched....

I got it to compile a while ago, the mistake was all my fault not realising you code was using the built in SD card and not the SD care from the audio shield.

From my test so far I'm not getting great quality results on 3.2, very crakly/bitty, I think talking to the audio SD card over SPI may be causing some performance issues. Not sure if accessing the built in one on 3.6 performs a load quicker and therefore gets better quality results.

Will get my hands on a 3.6 soon enough and test!

[bobkruijer]

I got it to compile a while ago, the mistake was all my fault not realising you code was using the built in SD card and not the SD care from the audio shield.

From my test so far I'm not getting great quality results on 3.2, very crakly/bitty,

I also got it to work on a 3.2 using audio shield SD card. I'm also getting some crackly sound, but weirdly enough I cannot change the 'rate' when the file is playing. It seems to poll the analogread at startup but once it plays it almost seems like the sketch gets stuck?

Any clue as to where I should be looking to solve this? I am using the entire forked audio folder and can compile without errors.

[propa]

I also got it to work on a 3.2 using audio shield SD card. I'm also getting some crackly sound, but weirdly enough I cannot change the 'rate' when the file is playing. It seems to poll the analogread at startup but once it plays it almost seems like the sketch gets stuck?

Any clue as to where I should be looking to solve this? I am using the entire forked audio folder and can compile without errors.

Yes that sounds like my experience too, checked the serial monitor and the sensor data looked like it was being dragged through the monitor, wouldn't rest when pot was at 1. and I couldn't get it to change rate either. I think it's due to the SD card, from what I've read now the 3.6 card has 6 dedicated wires, nothing is shared with the card, the audio shield SD card uses four wire SPI communication which is slower than the dedicated one on 3.6 or 3.5.

After a whole bunch of research yesterday Moo's seems like one of the more robust solutions, maybe bite the bullet and grab a better teensy? (apologies if that's not what you want to hear)

[bobkruijer]

Hmm, I kinda see how the speed access speed could be slower, but then I would expect a slower response- not no response at all to be honest. From what I understand it is not an official audio lib, so maybe it just doesn't work well across different teensy models? Be that as it may, I'll probably will grab a 3.6 just to try if it works for my purposes, would be keen to hear your experience on it as well!

[SpeakingInTones]

I moved the variable playback rate feature to its own branch here https://github.com/newdigate/Audio/t...-raw-resampled

I've briefly tested the code, seems to be okay between -1.0 and 1.0, posted quick video https://www.youtube.com/watch?v=rEEJf7q9tRY (apologies - its pretty raw)

If anybody has the time and inclination, I'd be interested to know your thoughts/experiences/questions...

Im planning on using this feature with a tempo synch'ed teensy audio recorder/looper... Also like to see if I can get it to work with .wav files

If you ever go to Vegas, I owe you a beer. You just helped me clear a project that has been clogging up the project bin for more than a year. THANK YOU!

[Moo]

If you ever go to Vegas, I owe you a beer. You just helped me clear a project that has been clogging up the project bin for more than a year. THANK YOU!

Awesome, Im really glad to hear that!

There is still a little bit of work required - when playing in reverse and the pointer reaches zero, it currently freezes. It should be fairly easy to fix, just haven't had much time to spend on it lately. At some point in the future I will need to sort this out for myself. Also wanted to play mp3 with variable playback rate one day too...

[SpeakingInTones]

I noticed that about the reversing. For my application I needed to go faster or slower but never backwards, so I changed your example code for the knob read like this:

 if (newsensorValue != sensorValue) {
            sensorValue = newsensorValue;
            PitchAmount = (sensorValue + 255) / 512.0;

I just basically futzed with the numbers until I was able to get it where I wanted it... But that does bring up 1 question that I had: I wasn't able to get that to work by doing a simple map. For instance this:

double rate = map(sensorValue, 0, 1023, -0.99, 0.99);

didn't seem to work... maybe due to the negative numbers?

Also is it possible to use this with the onboard memory? Like if I encode the RAW file into .cpp/.h files?

Thanks again!

EDIT: just tried this:

PitchAmount = map(sensorValue, 0, 1023, 0.5, 2.5);

it seemed to play high pitched, in the middle and not at all... was weird.

[Moo]

Not sure about map function...

If you want to use variable playback rate using memory, you would need to slightly alter the source code, play_serialflash_raw.cpp in the audio library. Or better, copy the .h and .cpp to a new class name, and do adjustments in the new class.

I found it easiest to introduce an intermediate class - ResamplingSdReader - which behaves as regular stream reader, but internally does some resampling - see ResamplingSdReader::read(void *buf, uint16_t nbyte)

https://github.com/newdigate/Audio/c...095264e84da429

Hope this helps.