[jtwrace]

I'm curious to know what measurement(s) should be taken on a preamp or amp that there is a direct correlation on sonics. 

[Mitsuman]

This should be good. 

[Ethan Winer]

I'm curious to know what measurement(s) should be taken on a preamp or amp that there is a direct correlation on sonics.

Only four parameters are needed to define everything that affects audio fidelity:

Frequency response
Distortion
Noise
Time-based errors

In truth these are parameter categories, with several subsets each. For example, under noise is hiss, hum, and cross-talk. Under distortion there's THD, IMD, and aliasing, among others. Time-based errors encompass wow, flutter, and jitter. But these four categories tell all. The ultimate test is the null test, where the output of a preamp or other device is subtracted from its input to reveal all differences.

--Ethan

[jtwrace]

Only four parameters are needed to define everything that affects audio fidelity:

Frequency response
Distortion
Noise
Time-based errors

In truth these are parameter categories, with several subsets each. For example, under noise is hiss, hum, and cross-talk. Under distortion there's THD, IMD, and aliasing, among others. Time-based errors encompass wow, flutter, and jitter. But these four categories tell all. The ultimate test is the null test, where the output of a preamp or other device is subtracted from its input to reveal all differences.

--Ethan

Is this an industry standard or an Ethan standard? 

[Ethan Winer]

Is this an industry standard or an Ethan standard?

What do you think?

Look here and draw your own conclusion:

www.ap.com

--Ethan

[jtwrace]

What do you think?

Look here and draw your own conclusion:

www.ap.com

--Ethan

I likey.  I wonder how many companies use this though.     Do you happen to know?  Do you own one?

[Ethan Winer]

I likey.  I wonder how many companies use this though.     Do you happen to know?  Do you own one?

I like it too, but no way can I justify that sort of expense. Fortunately, one can do real testing with a high-quality sound card, audio software that offers FFT analysis (many do), and a little ingenuity. An entire chapter in my upcoming book talks about this.

Anyway, all serious audio manufacturers and developers use this level of test gear for confirming their products. Here's another:

http://www.prismsound.com/test_measure/test_home.php

--Ethan

[JohnR]

Which category is a waterfall plot in?

[Ethan Winer]

Waterfalls assess time-based phenomenon such as ringing. But room acoustics itself is not really a parameter for audio gear because echoes, reverb, and modal ringing happen outside the gear. Then again, ringing can occur within gear, so a waterfall could be used for that.

--Ethan

[dmatt]

Ethan,

Would a null test on an amplifier assume a stable and constant load?  Would that mean that we would still have to use other tests to get an understanding on how the amp behaves with speakers?

My question is not intended to argumentative, I'm just trying to make sense of all the info I read on the web and the bathroom walls of the audio stores.

David

[Ethan Winer]

The beauty of the null test is it can be run in situ. So you could connect a speaker and also null the input and output signals. In fact, that's probably the best way to do it, to satisfy those who believe that a varying speaker impedance is a factor.

--Ethan

[dmatt]

Ah hah!  

Makes sense.

Thanks.

The beauty of the null test is it can be run in situ. So you could connect a speaker and also null the input and output signals. In fact, that's probably the best way to do it, to satisfy those who believe that a varying speaker impedance is a factor.

--Ethan