Suitability of AD3 as digitizer for the vhs-decode project

[joebobjoe]

I've recently embarked on a project to digitize my family's VHS tapes, aiming for the best possible image quality. In my quest for an optimal solution, I came across the vhs-decode project, which involves tapping a test point inside the VCR and using recommended devices like a hacked capture card or the Domesday Duplicator to capture the "VHS FM" signal to a PC.

However, I've noticed that some of these devices have deficiencies, prompting users to design their own PCB, such as the SMIRF. This led me to explore alternative devices, and that's when I discovered the AD3.

According to user feedback, storing data from VHS is most effective at 20 msps with 8-bit resolution. Additionally, users suggest that the digitizer should have a low-frequency response down to 1 kHz, a feature lacking in many devices recommended on the vhs-decode wiki.

So, my questions are: Can the AD3 handle the throughput of a 20 msps 8-bit signal over USB? And does it have the capability to digitize frequencies down to 1 kHz?

Edited January 6 by joebobjoe

[attila]

Hi @joebobjoe

The AD3 can capture at up to 125MHz on up to 2 (8) channels up to 64k (2x32k) sample device buffer. The record streaming is also sampled at 16bit/channel, can work at up to 10MHz on 1 channel, 5MHz 2 channels. The inputs are differential and DC coupled, with BNC adapter single ended and AC/DC switch.
The ADP3x50 and EclypseZ7 have device buffer of 128/256Mi samples, allowing to capture up to 125MHz on up to 4 channels.

[joebobjoe]

Just to clarify, record steaming at 10 MHz (on one channel) means 20 msps of 16-bit data?

[attila]

Hi @joebobjoe

No, 10MHz on 1 channel is 10Msps.
The samples size is always 16 bits/ channel, 14 bit at up to 125MHz ADC + 1 or 2 bits for lower rates from averaging of multiple ADC conversion.

[joebobjoe]

On 1/10/2024 at 5:26 PM, attila said:

Hi @joebobjoe

No, 10MHz on 1 channel is 10Msps.
The samples size is always 16 bits/ channel, 14 bit at up to 125MHz ADC + 1 or 2 bits for lower rates from averaging of multiple ADC conversion.

Is there any way you could add support for 20 msps at 8 bits/channel? Then AD3 could be used for the vhs-decode project.

[joebobjoe]

Are there any considerations to enhance the bandwidth for recording and streaming? It feels like the current setup necessitates investing in a more expensive Digilent device for higher performance.

Expanding the digitizer capability of AD3 to fully utilize USB 2.0 bandwidth could be a valuable improvement.

Why can't Digilent just open source the dang thing if it is for learning?

[attila]

Hi @joebobjoe

The AD3 has multiple parallel running instruments which share the same communication channel, so the data streaming (record/play) is performed in chunks. Due to the latency the streaming can use about half of the communication bandwidth, 10MSps = 20MBps = ~40MBps/2
The ADP3X50 has DDR-RAM, which lets you capture up to 128Mi samples on up to 4 channels at up to 125MHz. Even longer records on this device can almost fully utilize the USB/Eth bandwidth tanks to the larger chunks allowed by deep device buffer.
The EclypseZ7 with Zmod-Scope, AWG... is a development board which can be also used similar to ADP3X50 with WaveForms.