Make a good measurement system with REW and Raspberry

MadSc1

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Nov 7, 2019
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Really cool !! I agree wholeheartedly about the utility of the RPi. It is such an amazing tool !!! I am making amplifiers and recording equipment which is more for character than 100% linearity. So finding tools that help me 'characterize' the interesting contraptions I make are extremely helpful. Your posts are like gold !! I mention that to encourage your efforts and sharing.. Also to let it be known that even though people may not vocally appreciate all the time >> you are appreciated. your efforts are important and cool. Blazing new trails is not exactly 'trivial'
 

Antonio Di Motta

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Thank you very much for the encouragement, I have been working on the 4.0 version of the tool for more than a year, which should have professional features. I am currently involved in the design of a sound card dedicated to the raspberry Pi 4.0 with characteristics of low distortion and high linearity and sampling frequency of 192 Khz. I hope to be able to present it in the first few months of 2020 my performance terget is to overcome the Clio audiomatics card, if I succeed I will be very satisfied ..
Thanks again
Antonio Di Motta
 

WesB

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Aug 27, 2018
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Hi Antonio:

Just to let you know, you are not alone. For quite a while I have been using the Raspberry Pi Zero with a couple of the AudioInjector boards. I had sponsored (kickstarter) the AudioInjector stereo card at 96khz and the AudioInjector Ultra 2 card at 192khz. I wanted no less than 192khz and 24 bits.

Problem with the Ultra 2 card is that it is not set up as a sound card with line in and line out levels. I created test files at max loudness with Audacity and measured something like 32 v peak to peak from the outputs with my oscilloscope. Like you I then started to search for other sound cards for the RPI Zero and wound up with the Hifiberry DAC+ADC Pro.

The Hifiberry unit glitched when I first tried a REW sound card calibration. A very quick response from Daniel at Hifiberry suggested the glitch was fixed but not yet in the download version of Raspbian (Raspberry Pi version of Debian). He suggested I do a:
rpi-update
to update the kernel. The results was a very flat REW sound card calibration.

The Raspberry Pi Zero has plenty of power for the 192khz 24 bit boards when run as a set of alsa commands in terminal mode (aplay and arecord). When playing in Audacity from the desktop, it runs close to 100% on the cpu gage of the desktop while the terminal command of aplay of the same file maxes out at about 14% .

I still need to use REW to set up my 12+12 band Equalizer to equalize my listening room but it hasn't been fruitful so far.

Another add on to the use of the zero and sound card is to capture vinyl at 192khz 24 bit when I receive the boards based on audiokarma's forum on a RIAA pre- amp.

I think we would agree that there is a lot of power in an SBC that is smaller than 1.5 by 3 inches.

I appreciate the time and effort you put into this thread.

Wes Brenner
 
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Antonio Di Motta

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Hi Wes Brenner,
I did a lot of tests with the Audioinjector sound cards (Zero and Stereo) and unfortunately I came to the conclusion that they have instability of the frequency response and they are also very noisy.
As for the Raspberry I use the Pi3 Pi3 + version and most recently Pi4, the REW software requires more processing power than the Pi 0 version.
The Hifiberry DAC + ADC Pro sound card certainly corrected a problem they had on the previous version Hifiberry DAC + ADC which had too high an input capacity that limited the frequency response very much.
I had reported this problem to the technical department, but they ignored me, after a short time they changed the card and the characteristics they declare on the Pro seem good.
Currently I am busy designing a sound card based on the Cirrus Logic CS4272 sound chip and I hope to be able to test it as soon as possible to verify correct operation.
Regards
Antonio
 

WesB

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Aug 27, 2018
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Hi Antonio:

Another similarity of our equipment is the linkwitz mod of the wm61a Panasonic mic capsule 2 wire connection (part C in diagram of message number 33 of this thread). Back in the day there were rumors that these capsules (or the wm60a) were so good at bass response they were used for measuring rumblings in volcanoes. Sadly, Panasonic quit producing these gems that were about $2 apiece. Please keep us up to date on your work on the CS4272.

I haven't come across a problem with REW and the Raspberry pi zero but I may be using a different operating system.
I use the most recent release of Raspbian on the RPi zero which is named Butch. For those non linux users, major upgrades to Debian are toy story character's names and Butch is required for the RPi 4.

Wes Brenner
 

Antonio Di Motta

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Hello
I have been using Rew with Raspberry for at least three years and I started working on my project with the Pi3 version, with the Pi zero version I have never tried considering it too underperforming to use with REW, especially when it has to perform calculations for the Waterfall or for display spectrogram or when it has to calculate and display RT60 Decay.
With version 4 with 4Gb of memory these functions are quite performing, I would be curious to see how a Pi zero works but I think it can be much slower.
Currently, for version 4.0 of the instrument, I am using Raspberry Pi4 with Raspian Buster updated to the latest version with kernel version 4.19.97-v7l + # 1294 SMP Thu Jan 30 13:21:14 GMT 2020.
The previous version of the tool 3.0 (that of the post) I used Raspberry PI3 with OS. version Xubuntu 16.04.

Regards
Antonio
 
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