I have just done some "research" on the much discussed decay noise/distortion on the XP/JV synths, and I thought I should publish my findings. I own an XP-60 that I used for these tests.

As the sound on the XP-60 decays, a slight noise/distortion may appear. Some users have blamed this on the D/A-converters, others on the synthesis engine itself.

I used a piano-patch that I know has this noise on the decay. In tone 4 of the patch, I included a sine waveform and assigned it to the lower part of the keyboard. I limited the piano to the upper part, so that I got a split. I adjusted the sine so that it was in a different part of the frequency range than both the piano and its decay noise. (A sine only contains one frequency, so that it is easy to separate from the decay noise and the piano). I turned the tone volume of the sine down really low, as I have to turn up the volume of my amplifier to hear the decay noise at all.

I then tried to play a note with the piano patch, and let it decay. At the same time I increased the volume of my amp towards max. As the decay noise/distortion appeared, I tried to tap a key on the lower part of the keyboard, assigned to the sine waveform. With brief taps on the key with the sine, I could clearly hear the decay noise disappear! It reappeared the moment I released the sine.

From this I conclude:
The decay noise is not in any way related to the synthesis engine itself. The noise/distortion appears when the TOTAL signal-level of the output drops below a certain level. I have heard users complain about hearing the decay-noise all the time while playing e.g. sequenced songs. This must be a problem of their hearing, or the placebo effect!

The decay noise does NOT appear at the end of every note played, and is not really related to decay (in the synthesizer meaning of the word) at all. It is only related to the outputs. This means that in a typical sequenced song, the decay noise will appear for the last 2-3 seconds of the song, when the total level is dying!! Other than this, the outputs will mostly perform perfectly. Playing in patch-mode (with percussive instruments), the noise may appear slightly more often.

Decay noise of this kind seems to be quite typical for digital instruments, exactly the same symptoms were discovered in a Technics KN-920 keyboard.

It may not even be the D/A-converters that are to blame. Perhaps there is something in the analog part of the output?

Some users have claimed that this very minor fault in the XP/JV-synths make them unusable for professional purposes. Well, if it's pro enough for Jean-Michel Jarre (XP-80 on Metamorphoses), I must admit that it is more than pro enough for me!!! But perhaps we have some REAL pros on this message board? :-)

Hope this information was useful.....

Stig

Stig, appreciate the info, as I have never noticed the decay myself. I must admit that my JV-2080 is more than pro enough for me as well. Keep on rockin'.

Of course, all "studies" need to be replicated, so I performed the same experiment with my XP-80, but listened through headphones via the XP-80's headphone jack. Of course, because of the low volume level of the "decay noise" (abbreviated "DN" from here on), I had the volume slider in its maximum position and had to elimate all other sources of noise in my house. I used Sony MDR-7506 phones for monitoring, by the way.

Basically, I picked a 4-tone piano patch off of the Session exp bd that I knew "had" the DN. I also assigned a sine wave(form) from the Vintage Synth exp bd (071) to the fourth tone, replacing the preset fourth tone selection. Then, I mapped the tones out on the keyboard as done by the primary researcher, stigf, and listened to how the DN responds in the various situations originally described. With the volume level of tone 4 set at 40, the DN was eliminated by pressing a "sine key" (sounding the sine waveform), but I could still hear the DN with tone 4 vol. level set at 20. I'll give more info in the next post; my computer has been booting me offline recently and I don't want to lose all I've typed...

(cont.) Furthermore, when I panned the sine waveform/tone 4 fully to the right, I still hear the DN from the piano sound (which is heard equally L and R) in the left headphone while the sine waveform is sounding/being played.

Then, there's the effect reverb has on the DN - reverb ("Hall 1") lengthens the duration (time) of the DN considerably (3 times or so longer), like the DN is reverberating as well as the waveform sound. (N.B. I know nothing of the physics of sound; I'm only reporting what I have observed!) Try this, stigf: Assign a sine waveform to a tone of a patch and mute all other tones of that patch (in your original experimental patch, mute tones 1-3). Set tone 4 volume level to 127 and pan to 0, then set the TVA ADSR envelope so that there is no S or R (attack: time - 0, level - 127; decay: time - 127, level - 127). Play the sound with the reverb (Hall 1) on, then off. With sustain and release set to 0 on the TVA envelope, I can easily hear the DN with reverb ON, but cannot hear it at all with reverb OFF. The same thing happens with other waveforms/tones with TVA envelopes set for AD only.

I don't know what all of this means, but thought stigf and others might be interested. Thanks for the original research, stigf! Best post on this BBS in a while!

As stigf mentioned and as I mentioned in a previous post on the "...ends in distorted fuzz" thread, it is really hard to notice the fuzz in the course of "normal" playing, sequencing, and recording. I had my XP80 for two years before noticing the DN and only noticed it because I went looking for it. I just bought an XP50 to take on the road (so my XP80 can stay in the studio) and it does not have the DN; however, I may have to sell it and get an XP60 with the DN for other reasons (read: the DN does not bother me!).

Thanks alot for the positive response to my posting! I agree with you Wilkes, the DN appears stronger when the reverb is on. I believe this has to to with the fact that the reverb makes the total signal decay slower, so that it spends a longer time below the "critical level". If the level drops fast, it will spend shorter time in the critical area, and the noise gets less audible. The fact that the DN appears also when only reverb is present, rules out the possibility of the DN coming from the synthesis-engine itself.

I think the most important part of our discovery, is that the DN will not be present when the level on the output is above the "critical level". And it is not just that it is difficult to hear it; it is not there AT ALL, not even teoretically. This means that my sequenced songs have NONE of this noise until the end of the song. I can live with that!

Nice work Wilkes!

Stig