Doubts about Multi-instrument

Doubts about Multi-instrument

Postby Eduardo » Mon Mar 07, 2016 10:07 pm

Hi dear,

I intend to order the Multi-Instrument to proceed audio equipament tests.
Is it possible to measure the frequency response up to 50Khz?
What is the lowest S/N that it cam measure?
Is there an ADC/DAC that can be used in PC (USB) to improve the precision?
Is it possible to get these parameters usind a oscilloscope USB like the VT DSO-2810R with the Multi-instrumento to get more accurate and extended measurements?

Thank you very much.

Eduardo
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Re: Doubts about Multi-instrument

Postby VirtinsTech » Fri Mar 11, 2016 1:01 pm

Thank you for your questions.

1. If you use a sound card to measure the frequency response of a DUT (Device Under Test), you can measure up to 96kHz if the sound card has a sampling rate of 192kHz and a bandwidth of around 96kHz. Please check the sound card's specifications. You can also use our products VT DSOs to measure the frequency response of a DUT. These DSOs have an analog bandwidth well above audio frequency range.

2. The lowest S/N it can measure depends on the hardware used. If you use a sound card for audio measurements, you can do a loopback test to check the audio parameters of the sound card itself first. Some examples are here:

http://www.virtins.com/doc/D1004/EMU_Tr ... _D1004.pdf
http://www.virtins.com/doc/D1007/EMU_0204_Report.pdf

Audio parameters such as noise level and distortion cannot be compensated using software, and thus the quality of the measurement hardware must be better than the DUT in order to get meaningful results. On the other hand, frequency response can be compensated by the software .

3. Our current USB Oscilloscope products are well suited for audio frequency response test. When they are used for THD and Noise measurements, please bear in mind that they can only be used to measure those DUTs which have worse performance than the USB oscilloscopes. Please check the respective USB DSO's specifications.
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Re: Doubts about Multi-instrument

Postby Eduardo » Wed Mar 16, 2016 4:01 am

Do you consider that use an oscilloscope USB is more recommended for my intention?
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Re: Doubts about Multi-instrument

Postby Eduardo » Wed Mar 16, 2016 4:03 am

I liked DSO-2810R.
Specifications inform that it can be used in conjunction with Multi-instrument. Is it the best solution?
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Re: Doubts about Multi-instrument

Postby VirtinsTech » Thu Mar 17, 2016 7:41 pm

It depends on what you want to measure. VT DSO-2810R does not contain a built-in analog signal generator. But you can still use its MLS (Maximum Length Sequence) output from the probe calibration output to measure the frequency response of a device under test (DUT). Alternatively, you can use the computer sound card as the signal generator to generate the test signal. VT DSO-2810R is good for audio frequency response test, but it is not suitable for measuring the THD of a HiFi audio device due to its own THD level.
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Re: Doubts about Multi-instrument

Postby Eduardo » Thu Mar 17, 2016 10:23 pm

And can MI measure low levels of THD and noise?
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Re: Doubts about Multi-instrument

Postby VirtinsTech » Mon Mar 21, 2016 7:15 pm

Multi-Instrument is well suited for low THD and noise measurements for HIFI audio devices. The lowest distortion and noise that can be measured is practically only dependent on the measurement hardware used, e.g. sound cards, VT DSOs, NI DAQmx cards, etc.. The distortion and noise introduced by the numerical computation of the software itself is negligibly small even compared with the best precision measurement hardware available today. The following screenshot shows the distortion and noise introduced by the numerical computation of the software itself (24-bit ADC and DAC precision). It shows that the THD+N is only -146dB. In the screenshot, software loopback mode "iA=oA, iB=oB" is used without any involvement of the sound card hardware.

THD+N.png
THD+N.png (172.24 KiB) Viewed 18302 times
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