I have a question on Analog Out.

[James Choi]

I am using a USB DAQ - USB6221.

I am trying to develop a pure-tone generator with different intensity levels.

Analog-out is directly connected to a headphone, and the range of intensity is from 5dB to 100dB SPL at 1kHz.

There is no problem to make a pure-tone with 40dB SPL or above.

When I reduce the value to control the Analog-out for making a low-intensity tone, I can not hearing any sound.

I think that it is related to the resolution of DAC on board.

Should I use an external amplifier for completing my job?

Is it impossilbe to change the gain of the internal amplifier connected to the output of DAC on board?

Please, let me know the solution.

Thank you.

[Abhinav T]

James,

Unfortunately the PCI-6221 does not have programmable output gain. You will have to use an external amplifier.

[James Choi]

Is there any model with Analog Output Programmable Gain?

Please introduce it to me.

Thank you for your reply.

James CHOI

[ChrisR.]

Another idea would be to add dither to your signal before sending it to the analog output channel. That should keep the bits moving enough to allow you to generate tones well below 1 LSB pk-pk.

Have you verified that the level at which the sound disappears corresponds to the resolution limits of the analog output channel?

Chris

[Abhinav T]

Hi all,

I do not think that dithering will actually work to improve analog output accuracy.

You best bet would be to purchase either a NI 628X series board or NI 4461 board. Both of these board have selectable ranges for output and thus will apply appropriate gain amplifiers for maximum resolution.