NEW Jitter tests showing the effects of Intersample Overs

[Tranquility Bass]

The following Jitter tests illustrate the benefit of using the built-in Inter-sample Overs Guard in preventing internal numerical overflow inside the asynchronous sample rate converter of the SHARC DSP. We used the same J-test methodology that we used for our other tests.

Firstly the following shows the scope screen capture of one channel of the output of the Preamp with the J-test signal from the analyzer applied directly to the USB port of the Preamp. For all intents and purposes, it should look like a 12kHz sinewave but because of Intersample Overs, there is internal overflow in the sample rate converter which manifests itself as waveform distortion similar to clipping which is a side effect of upsampling or interpolating to a higher sampling rate.



The following shows the resultant FFT spectrum and notable artifacts can be observed.



Expanding the frequency scale of the spectrum above shows in much more detail the problems caused by the inter-sample overs.



With the Inter-samples Guard switched on we noted how many times the sample rate converter was overloading in the statistics collecting mode ! Once activated the Guard reduced the signal input level to avoid any more internal arithmetic overflows and reported that the signal had to be reduced by 3dB to achieve this.



And the signal from the output of the Preamp was reduced in amplitude by 3dB but is no longer visually distorted!



Now let's see the effect on the J-test spectrum from the analyzer. A vastly much improved and cleaner spectrum is observed below when the sample rate converter is not overloading and essentially proves how transparent the SHARC sample rate convert can be !



The expanded frequency scale of the above FFT spectrum is shown below !

[Tranquility Bass]

An excellent article

New Test Reveals How Vintage CD Players Outperform Modern Models Thanks to One Forgotten Design Choice

The study shows how overlooked testing methods hid the true performance of both vintage and current models.

Lab tests have long been the final word on how CD players perform. Yet those tests rarely went beyond a few single-tone checks, leaving out the kinds of stresses that music actually creates.

Recent testing by NTTY filled in the gaps with a method that looked at clipping, distortion under load, and how digital filters behave with shaped dither. The results changed the story of how older non-oversampling and newer oversampling players really compare.