Audio oscillator with SPDIF or Toslink output - Page 1
Forum section: electronics / projects

author: Circlotron
author_rank: Super Contributor
timestamp: April 22, 2018, 11:17:29 am
content: I have a fairly reasonable quality DAC that I used to use between my CD player and amplifier. Don't really use it nowadays, and seeing it has a distortion at max output of 0.0018% I thought it might make the basis of a good audio oscillator to 20kHz max. Just needs to be driven from a SPDIF or Toslink source that is generating the actual frequency. Is there such a source?

author: The Soulman
author_rank: Super Contributor
timestamp: April 22, 2018, 01:27:01 pm
content: Cheapest and easiest would be to use computer with one of the many generator programs available freely incombination with a usb to spdif interface, make sure it supports the resolution you want, as the cheapest ones generally max outat 16bit 48KHz.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 22, 2018, 02:09:30 pm
content: You can use a FPGA board.

author: Circlotron
author_rank: Super Contributor
timestamp: April 23, 2018, 12:24:26 am
content: Quote from: The Soulman on April 22, 2018, 01:27:01 pmI do have one of those, a cheap one though, and while it works it produces a chk-chk-chk noise on the output along with the desired signal. I don’t know how many different ones I would have to buy until I found one that worked properly.

author: hamster_nz
author_rank: Super Contributor
timestamp: April 23, 2018, 12:55:18 am
content: A Raspberry Pi, or even an ESP32 and something based aroundhttps://d3uzseaevmutz1.cloudfront.net/pubs/proDatasheet/CS8406_F6.pdfcould be an interesting project.Because it is optical, Build quality doesn't have to be spectacular for good results. Perfboard for the win!

author: Zero999
author_rank: Super Contributor
timestamp: April 23, 2018, 07:47:21 am
content: Quote from: Circlotron on April 22, 2018, 11:17:29 amHow is that possible? That looks like marketing to me.The resolution of a 16-bit audio is less than that.

author: Circlotron
author_rank: Super Contributor
timestamp: April 23, 2018, 10:50:13 am
content: Quote from: Hero999 on April 23, 2018, 07:47:21 amMaybe the distortion figure is for 24-bit mode?Anyway, this is the unit ->https://archive.org/stream/Silicon_Chip_Magazine_2009-09_Sep#page/n13/mode/2up

author: BradC
author_rank: Super Contributor
timestamp: April 23, 2018, 11:37:18 am
content: Silicon Chip also did a neat audio generator that had an SPDIF output. Altronics used to sell a kit for it, but now I check and it's gone. It was a pretty neat unit, but the kit was $$.

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 23, 2018, 02:33:39 pm
content: To benefit from your low distortion DAC, you need a low distortion generator. Less trivial than it seems.You didn't mention what kind of signal you want to generate? Pure sine? Other waveforms?There are pretty expensive units, such as this:https://www.nti-audio.com/en/products/digirator-dr2(Probably not worth it if all you want is to reuse your DAC.)As others have suggested, a PC/ or SBC-based solution is probably your best bet for a simple and low-cost approach, yet with the ability of generating low-distortion signals. If you have access to I2S signals on your DAC, you may not even need an additional SPDIF board (some SBCs have I2S built-in).You could also do this with a microcontroller or an FPGA, but there will be significant dev time, especially if you want some kind of UI.

author: _Wim_
author_rank: Super Contributor
timestamp: April 23, 2018, 07:55:01 pm
content: Quote from: Circlotron on April 23, 2018, 12:24:26 amMake sure you levels are not clipping. Try lowering the level in your software package, this could be the reason of the noise...What software package are you using? I had good luck with Room Equalizer Wizard (REW) in the past, which is freely available