I have been using the QA401 and its software for almost a year now, and I have a few suggestions regarding the test plugins that I think will improve them.
The first thing that has bugged me since I first started using the QA401 is the lack of certain options in the test plugin menus, in particular the frequency response tests. The lack of the ability to enable averaging comes up while I am performing a response sweep on a tape recorder, where there are always small deviations occurring because of the physical nature of the media. Being able to apply a 10 average makes for a cleaner graph to provide my clients.
The second item that I think needs to be implemented is the ability to change the vertical axis in the test plugin menu for the tests that use dBV as the scale. Many pieces of gear these days use dBm (0dB=775mV). Having to adjust the external gain setting and changing the axis name manually seems more like a workaround and not a solution.
I think, overall, that the majority of issues I have are with the lack of consistency between the main screen options and the test plugin options. The inability to properly title and add notes to the main screen printout is limiting, especially when I would like to use averaging and other items available in the main screen menu.
This is not to say that I do not like the QA401 experience thus far, but I do think that these are some improvements that I think will make the experience even better. Huge shoutout to Matt and the whole QA team for the regular blog/forum posts and software updates
There’s always a tradeoff in the plugins in terms of how many options can be shown. There’s an attempt to striking a balance between what is most needed in the plugins and complexity. If every plugin surfaced every option, then it’s a long, long list of options that would be a bit daunting to most. Sometimes I think it’s better just to add another plug-in rather than adding too many options to a single plug-in.
With averaging, remember that FFT size will also average imperfections. A 256K FFT should be pretty similar to averaging 32 8K FFT (32*8).
The 2.0 release of the software will do better with units, but the plugins will very much still want to speak in dBV and the offset method previously outlined will need to suffice for the near and mid-term.
Below is a link that might help speed up frequency response measurements on a tape player. You’d basically create a WAV of a special chirp, then record that using your best “reference” deck, and then play the special chirp back on the deck you are testing and you should get the overall frequency response of the reference deck (used to record) and the DUT (used to playback). Of course, if you are already using a test tape with reference tones, it’s tough to beat the certainty there. But there could be a good time savings for intermediate checks. You could do a full freq response chirp in a few seconds. And also save wear and tear on your reference tape until the final test was needed.
Hi
I also agree that I should like to have the possibility to use dBu in stead of dBV. Traditionally, dBV has been used in US and Asian countries, while dBu has been more common in Europe.
(Many people want dBm, but dBu is of course more correct since dBm is a power unit, not voltage. 0dBm = 1mW. Only at 600ohm load, 0dBm = 0.775V. At 50ohm, for instance, 0dBm = 0.224V. 0dBu = 0.775V regardless of load impedance).
Otherwise, thanks for very useful products at reasonable prices!