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Which tools - oscilloscope/logic analyser/soundcard for DIY audio products
Which tools - oscilloscope/logic analyser/soundcard for DIY audio products
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Old 1st February 2018, 11:54 AM   #1
crestaboy is offline crestaboy
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Join Date: Jan 2018
Default Which tools - oscilloscope/logic analyser/soundcard for DIY audio products

Hey all

New here and a bit of a newbie to audio but this forum looks excellent and I have done some searching but been unable to find conclusive answers.

I'm working on a musical instrument which plays out audio signal in a small space. Think the body of an narrow whistle or so - so I don't have much width to use, perhaps 14mm at max.

Currently I am using an atmega328 chip and the on chip DAC but know I need to upgrade to get much better sound quality.

Therefore I am thinking of using the chip from a teensy as an I2S controller and something like an STGL5000 to get 16bit sound. I am pretty confident I can design the PCB so it "works" but as for diagnosing the sound quality I am less certain.

I do not have the best ears and would prefer something more scientific than "it sounds nice".

Therefore - I need some way to do this. Doing some reading and thinking I was wondering if best way to do this would be to play a fixed/sweeping sine wave and measure the output and see how it compares for SNR. However I'm not sure the best way to do this, if a USB oscilloscope is suited - (resolution would need to be pretty high? - so maybe a sound card is better? ) and if so, which one?

Also have never worked with I2S before so wondering if a logic analyser is a good shout too - and if so, which one? I have a few hundred budget for the right tools but would like to save money where possible.

Also if anyone has good books/info sources on audio electronic engineering I would be super interested as right now all I do is hunt wikipedia etc and am a bit blind.

Thank you very much for all your help!
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Old 3rd February 2018, 05:45 AM   #2
1audio is online now 1audio  United States
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Location: SF Bay Area
Which tools - oscilloscope/logic analyser/soundcard for DIY audio products
Does the Atmega support I2S output? As long as you don't need to do some low level programming it should be pretty simple.

For the output chip a decent self contained chip like the AK4430 is a really good choice. It handles almost everything with few external parts, runs on 3.3V and sounds quite good.

Evaluating the sound of a musical instrument really is subjective. No instrument will tell you it sounds good. They are useful if it doesn't sound good to determine what to fix.

if you are reasonably skilled you can troubleshoot almost everything with a scope. For analyzing the sound a decent soundcard + software can be really helpful. If you program the chip for some specific pure sinewaves then FFT to look for distortions will tell you really quickly if its working right and not clipping. After that its all about the waveforms your trying to create and how your transducer interacts with the drive signal.

A dual trace scope is really all you need for I2S. Sync on word clock and zoom into the bit clock or data to see all there is to see. There isn't anything complex to decode.

Good luck.
Demian Martin
Product Design Services
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Old 3rd February 2018, 09:47 AM   #3
trobbins is offline trobbins  Australia
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Location: Melbourne, Oz
Can you perhaps summarise why you couldn't use a simple $1 USB mono soundcard? I have found the performance of the CM108 or CM119 based units is excellent for amplifier analysis, in that the frequency range can be extended way down to pretty much dc, and up to 20kHz is likely to suit your application, and snr is pretty much beyond 85-90dB, and basic loop THD is I suggest insignificantly low. And by judicious removal of the USB plug and 3.5mm sockets, the remaining pcb is getting quite small.

The pcb gets more onerous to play around with when using stereo or 7.1 channel versions, such as based on the VT1630A, although they can similarly be used for mono.

I'm unsure what interfacing you are really after. A good small electret is effectively a flat response reference microphone. There is so much free high-quality software as well as open-source tools based on windows OS - I'd be amazed if you couldn't find a simple path to take for whatever you want to specifically do.
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