Usable distortion analyser for Pre-/Amps

[Pjotr]

Hi,

Attached a loop-through result of what I archived with my (not that expensive) audio card. Averaging was 100 times. THD figure at 16 bits is –96db or 0.0015%, at 24 bits –111 dB or 0.0003%. More than sufficient for DIY projects IMHO.

As far as I can figure out, Audiotester takes into account the first 9 harmonics to calculate the THD number, but I am not sure. At 16 bits there are relatively large harmonics above the 9 th harmonic. So the THD number calculated at 16 bits is doubtful. Dunno with other software but the limit is the measurement bandwidth (< ½ Fs).

For THD+Noise it takes anything compared to the fundamental, so this will be more trustful I think.

Anyway the distortion profile obtained at 24 bits is very useful to judge the qualities of DIY efforts.

Cheers

[tschrama]

Hi Pjotr,

Those are excelent results! What soundcard did you use for that loop-through test?

Regards,
Thijs

[Pjotr]

Originally posted by tschrama
Hi Pjotr,

Those are excelent results! What soundcard did you use for that loop-through test?

Regards,
Thijs

Look at the top of the picture

Found that at Fs = 96 kHz distortion is worse (doubles). Also at higher levels than –6dB FS distortion becomes worse. I used a 10-cm loop-through cable. At long cable runs a lot of rubbish can enter the audio cables (i.e. from the mains cord), spoiling the results. Something to take care of.

Cheers

[tschrama]

Hi Pjotr,

I that 24bit -111dB number an absolute number or relative to -10dB. That would mean that the 5th harmonic level is -121dB. Your picture shouws the first harmonic somewhere between -110 and -120dB, not -121dB. Well, upon further inspedction, the red line is difficult to see but seems indeed to be in the -121dB ...

Thanks for the soundcard name.. looked it up.. on sale for 149.95$.. that nice indeed for such a high quality THD analyser...

Regards,
Thijs

[sam9]

I note the price is way below Lynx cards.

And even the M-Audio consumer card looks pretty good.

[IVX]

hi,
maybe try to compensate own sound card THD ? I has measurement my class D amp through motherboard AC97 gotten THD are 0.06%, loopback THD are 0.04%(@50hz-0.04%;@1khz-0.01%), and now through audigi i have THD-0.02%. I'll try to compensate FFT's in MsEXEL. What you think about it?

[Bricolo]

Originally posted by IVX
hi,
maybe try to compensate own sound card THD ? I has measurement my class D amp through motherboard AC97 gotten THD are 0.06%, loopback THD are 0.04%(@50hz-0.04%;@1khz-0.01%), and now through audigi i have THD-0.02%. I'll try to compensate FFT's in MsEXEL. What you think about it?

RMAA has a "susbstract results" option, but I haven't tested it

[IVX]

Hi,
RMAA has a "susbstract results" option only for two frequency responses, I've just tested it. For DIY measurement Spectralab 432 is much smarter.

[maylar]

What about frequency response tests? Do the soundcard software solutions have spectrum analyzers too?

And what are the requirements for hardware to get good results? I have a 16 bit Creative Labs PCI card... do I need more than that?

[wintermute]

Hi Pjotr,

I'd looked at Audio Tester V1.4 before and really didn't like it. Just downloaded V2 and it looks like it's much improved, both in functionality and UI wise. Though it looks like it's got a bit of a learning curve compared to RMAA.

Time to do some more playing me thinks

Tony.