Wednesday, 16 January 2019

Nearly finished Audio Oscillator

I have been working on a few issues with my audio oscillator. The latest is to get a higher output capability. I made an early test was with a LM386 amplifier, but it self-oscillated above 10kHz output (no idea why, maybe result of tangled bread boarding and no ground plane....). So I switched to a simple single transistor amplifier. I now get up to 10dBV output from 10Hz to 10MHz!!! Though I will probably limit the final design to 100kHz, it is an audio oscillator after all - and I do regard audio to go up to 100kHz as some instruments do produce harmonics up there.

IMG 0847

I have included a small attenuator in the AD8307 input to allow it not to overload at +10dB out, and adjusted the AD8307 software to be able to show output up to a 10dBV (2.3Vp-p). I have decided only to display the dBV value (to zero decimal places), not the Vrms one, as the calibration is not so easy or accurate


I have received a new AD9833 module - it's tiny, but works just fine. Now to design the PCB, purchase the case and build it...

Code Here

Sunday, 13 January 2019

Amazon Music - poor quality?

Over the years I have sought to reproduce music on my HiFi at the best quality I can.

The key to the whole affair is the ability to reproduce high frequencies, to give the correct timbre to instruments and wave form rise times for things like cymbals. It's not enough to have 20Hz to 20kHz as many instruments make sound well above that.

But, like the rest of them, Amazon Music streaming is very poor at higher frequencies, thus drums, cymblas and violins have no edge to them, even pianos sound bad. Look here, this is the spectrum of a music track from Amazon,

Screenshot 2019 01 13 at 19 24 11

You can see the abrupt sharp cut off above 16kHz. Quite useless for music reproduction. Even voices sound muffled.

Compare this to a track recorded at 96kHz/24bit - giving a theoretical bandwidth of just less than 48kHz,

Screenshot 2019 01 13 at 19 26 09

Now you can see what you are missing.

Frankly I think Amazon and other streaming services need to do much better. With the internet speeds we have now, enabling HD TV to stream, there is no excuse to ruin music in this way.

Sunday, 6 January 2019

Sythesised Audio Oscillator

While many struggle to build audio signal generators using phase shift networks, voltage and gain stabilisers and bunches of op-amps, there is another solution. Digital synthesis.

AD9833

The AD9833 is an IC designed for generating Sine, Triangle or Square waves from 0Hz up to +10MHz. It is simple to use with an Arduino to build a variable frequency sine wave generator. Combined with a Rotary Encoder and an OLED display an accurate audio generator can be made for about 20€!

Here's the circuit.

IMG 0835
And here's the mockup

IMG 0834

Code here.