A project log for DSP Field Mixer Recorder

USBmidi, bluetooth app controll 8 chan portable DSP mixer.balanced audio IO,phantom power,flexible routing,ISO recording. networked Timecode

ben biles 12/23/2016 at 17:122 Comments

great , finally the ADC DSP DAC is working. all channels working and tested I2S clocks up to 196khz 24bit and no clitches , jitter etc. fanout buffer working well. Eprom memory working in selfboot mode.

Its using about 350ma of power with all 8 differntial channels busy with on effect or other.

mix routing compression reverb eq's filters etc

The PGA2500 preamps work best without the ADC's 2.5v DC bias becasue of the lack of headroom at +-5v preamp rails so DC filtering capacitors are needed between preamp outputs and ADC inputs. I also have some resistors to attenuate the preamp's 8vpp to 5vpp of the ADC inputs. I think the ADC can handle 5.5vpp but don't want to blow the channels.

I'm not sure if I will work on hooking up the midi knob controller first or just make a blue tooth app to control the preamp GAIN / DSP functions / DAC output levels.

That would be a lot of knobs and buttons without a screen / menu. but adding rotary encoders and a cheap screen would be what all mixer recorders do already?

well there is a ton of work to do already with programing the mixer / microcontroller. I'm still just using an arduino ! I tried the edison but the I2C bus looked very week at 3.3v on my scope. I'm not sure if thats becasue there are 5 devices on the bus , I tried differnt value pullups and nothing really helped. Main reason for edison was idea I could record 8 channel TDM to SD card. Maybe this was a bad idea anyway. I prefer the idea all the code is just in the arduino IDE and would be even better if I could do the multichannel audio recording in arduino Due or Zero. Unlikely but worth looking at.

would be greatful if anyone can sugest a simple way to record either serial I2S or TDM audio to WAV files on SD card or SSD with just a simpe low power microcontoller ( pref without a full blown OS )

I suppose recording to a formatted card or drive woud require an OS of some kind?


ben biles wrote 12/23/2016 at 18:10 point

yes, that's the name i was  looking for :) could you recomend a good value AC coupling cap to use for this kind of application ? would I loose bass frequencies with a high value cap ? or other way around ? i'm using 10uf 25v, should i use tantalum , ceramic ? I suppose I could get a poor mans signal generator on the inputs ( for me an android app ) and put out a sweeping sign wave and look at the output of the preamp on the scope with differnt caps. Or AC coupling caps don't filer anything AC at all? my signal generator ( android ) is as good as useless i'm sure.. need to get a proper signal generator off of ebay one day maybe..

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K.C. Lee wrote 12/23/2016 at 17:31 point

>DC filtering capacitors are needed between preamp outputs and ADC inputs

Perhaps you meant AC coupling caps?

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