Zeddy plays guitar.

[Moggy]

Many moons ago (2007) I asked Charlie if it would be possible to play audio on the Zeddy. he replied that he didn't think we would be hearing Dark Side Of The Moon any time soon..

Skip forward 15 years and thanks to Adam it has come to pass.

So please welcome Zeddy, Mr Spand, a loose bunch of resistors, playing the lead break from the track "Time" by pink Floyd from the album Dark Side Of The Moon.

Maybe not Hi-Fi who gives a toss!! Nice through decent speakers.

[Lardo Boffin]

With the spiders from Mars?

Edit - sounds pretty good!

[Paul]

Very impressive.
Now please bear in mind that I have absolutely no idea about audio stuff,
Would it be possible to have the zeddy read a converted audio book?

[1024MAK]

If I’m understanding correctly, Moggy has been using a ZXpand or ZXpand+ connected to a resistor DAC.

The AY/YM sound chip provides a 8 bit digital I/O port. The eight I/O lines are used in output mode to feed the eight inputs of the resistor DAC, The output from this resistor DAC forms the audio out. One end of the resistor DAC connects to the 0V/GND from the ZXpand. This is also the ‘output’ 0V/GND.

See:

ZX81 playing SID-songs!

Zeddy Audio Jukebox

Zeddy audio playing now a reality!

So yes, although not CD or Hi-fi audio quality, and depending on the length of the audio book vs, the available memory, it could ‘read’ a converted audio book.

I’m sure Moggy, being our musical expert here, can tell you more.

Mark

[nollkolltroll]

No problem reading an audio book, the only limit is each track can be max 12.5 minutes long. Split into multiple files, and the next limit is rhe size of the SD-card. Not a tight limit

[Moggy]

Yes I found out the hard way trying to convert an entire album into one raw file!!!
Too many samples meant error C (maths overload.)

As for the quality I have found that soft or low volume sounds carry the signs of obvious 8 "bitness" whereas loud passages are quite listenable, so the main work to be done is in a WAV studio such as Audacity which following Adams instructions is simplicity itself.

@Paul.

I will try this with spoken audio and let you know result.

As Mark points out, yes it is a simple 8 resistor style "ladder" DAC connected to the B port of the AY unit on either classic or ZXpand +. The DAC apparently converts the 0's and 1's into a varying voltage that translates as audio.

As far as I know the "bits" are streamed from the SD card to the port with the timing having something to do with the hsync pulses although Adam can be more explicit on this.

The DAC I made is very crude as can be seen and close tolerance resistors should be use for better effect.

I did this as proof that it works and have sent off for a more professionally made unit C/W pre-amp which I have discovered is needed to make up for the volt drop that such a resistor network brings.

https://www.mikroe.com/r2r-dac-board


I believe Adam is looking into something called logarithmic 8 bit which apparently equates to linear 12 bit and something used on another old 8 bit computer, so should improve the audio even more.

A schematic of the DAC. The vertical resistors are double the value of the horizontal ones as far as standard values allow, and not too critical value wise. in my example 100 k and 47 k .

[David G]

the main work to be done is in a WAV studio such as Audacity which following Adams instructions is simplicity itself

Most impressive. And only took 60 moons! I've heard that song before, didn't we, didn't we

I take it you started with a CD audio file, and used Audacity to generate an 8-bit WAV file. Is the attachment an analog recording from the actual resister ladder?

[Paul]

In my opinion it's time for a zxpand++ DAC revision
Your adapter doesn't fit . Neither in size, format or color.

[Moggy]

@Paul.

Für mich geht das!

Hi Paul I have not forgotten about your audio book question and will work on this tonight. I also will question Adam as to whether it is possible to connect both ports A and B of the AY chip to the DAC and have 16 bit audio!

[nollkolltroll]

Moggy, forget about 16-bit audio. But it WOULD be possible to do 8-bit stereo... And possibly logarithmic u-law audio to get better/different sound quality.