Raspberry Pi 1 slight latency (solved with ChunkSize=256)

[saulstokes]

Hi! I just built a Minidexed and it’s working perfect except for one issue. It seems to have slight latency. I’m wondering if there’s any tweaks I can make to one of the files that can improve this or is it simply due to the type of Rasperry Pi that I have?

I am using a Rasperry Pi. P1 2011 Model B

I am just using a single voice right now.

Thanks!

[Banana71]

Hi Saul Stokes,

Yes, in your case it's the Raspberry Pi!

The chunk size is crucial for the latency and it is written to 1024 by default on the RPi 1. On all other Raspberry Pis the default value is 256.
I haven't tried whether a Raspberry Pi 1 can handle values ​​smaller than 1024. I would activate the "ChunkSize" line in the miniDexed.ini and see what happens. (Delete the # sign in front of the ChunkSize line.

minidexed.ini:

# Sound device
#SoundDevice=i2s
SoundDevice=pwm
#SoundDevice=hdmi
SampleRate=48000
ChunkSize=256
DACI2CAddress=0
ChannelsSwapped=0
# Engine Type ( 1=Modern ; 2=Mark I ; 3=OPL )
EngineType=1

With a Raspberry Pi 2 or better, the miniDexed is on a completely different level (8 TGs instead of 1 TG on a RPi 1) and I would definitely recommend it.

The program code that sets the chunk size as standard for the different RPis
conifg.cpp Row 61:

	if (m_SoundDevice == "hdmi") {
		m_nChunkSize = m_Properties.GetNumber ("ChunkSize", 384*6);
	}
	else
	{
#ifdef ARM_ALLOW_MULTI_CORE
		m_nChunkSize = m_Properties.GetNumber ("ChunkSize", m_bQuadDAC8Chan ? 1024 : 256);  // 128 per channel
#else
		m_nChunkSize = m_Properties.GetNumber ("ChunkSize", 1024);

[saulstokes]

OH this is fantastic. I'll play with this today! Thank you!

[saulstokes]

Just an extra note. I found a 20 dollar Pi 3 and ordered it so that if the latency fails, I can just move on to a newer one. Thanks again!
Saul

[saulstokes]

Just wanted to write a note and let you know that so far removing the hashtag seemed to fix the latency! Seems to be running fine. Thank you!

[probonopd]

Hi @saulstokes. Glad you were able to improve it, but now I am curious:
Removing which hashtag where exactly?

[Banana71]

The hashtag before ChunkSize in miniDexed.ini

ChunkSize=256

[saulstokes]

Yes I just simply removed the hashtag and saved. I believe this just forces the Mididexed to operate at 256. Works great. Absolutely no problems.

[probonopd]

If ChunkSize=256 works for all models, we might want to make it the default?

Or we could at least make it the default for RPi Zero and 1 if nothing else is defined. What do you think?

[saulstokes]

A little update. It’s been working fine but I recently tried to control the filter and resonance with cc’s and got radical stuttering. Doesn’t seem to be handling cc’s.

[Banana71]

A little update. It’s been working fine but I recently tried to control the filter and resonance with cc’s and got radical stuttering. Doesn’t seem to be handling cc’s.

Does this happen with the Raspberry Pi 1 or already with the Raspberry Pi 3?

[saulstokes]

Right now only the P1. I’m getting ready to swap for a P3 tomorrow so I can test this.

[saulstokes]

Just wanted to write one more comment. I upgraded to a P3. Banana71 you were right. It's so much more powerful. I'm blown a way. I also added the DAC which completely changes the quality of the sound. A total sonic jump also in terms of overall loudness. Thank you to all of you who worked on this. What a fantastic synthesizer! Mine is going into a battery powered live rig.