EastWest Ministry of Rock : crackles & clicks fixed on PowerPC

Posted: September 17, 2008 in Audio, Troubleshooting

Since version 1.0.083 of PLAY, performances of Ministry of Rock are far more better on PowerPC (G4 1,25 Ghz), thanks to some optimizing in the audio engine (better use of CPU resources) : the drum kits do not produce anymore CPU peaks, and the Telecaster Lead also benefits from the engine performance enhancements made by EastWest. The user interface is less demanding (in particular the vu-meters). The reverb still produces core audio overload after a few seconds, still randomly as with the previous versions (doesn’t seem to be completely tied with CPU power, perhaps more likely to a latency problem… that is a bit more complex). However it is acceptable from a G4, as the reverb algorithm is outstanding (and so very complex).

The main problem, audio crackles (and clicks on some samples) with Telecaster patchs (Lead and Chords), had to be fixed by two other means :

– first I received from EastWest support team (that I thank) new Telecaster Instruments patchs (that is mapping, not samples), that fixed the clicks problem on the notes I reported (some alternate samples from D#3, E3 et E4 on Telecaster Lead, etc.). In fact they simply excluded the wrong samples from the mapping, using samples from upper (or lower) half tone. A new MOR Instruments update (including these files) is planned, but there is still to know if it will only include Instruments patchs, or also new samples files (was the case for the first MOR update, that included new samples, and weighted 700Mb). However it would probably require new recordings (if clicks cannot be removed easily) and would then cost a lot (and would require the same recording conditions, not easy).

– secondly, after many new try, I noted that the persistant crackles that appear randomly (on various notes) when playing many notes simultaneously weren’t defects on alternate samples, but were more likely due to a latency problem. The CPU load wasn’t very high so I remembered what I reported in the soundsonline forums. I finally noticed that setting the sampling rate (playback) frequency to 48Khz or higher fixed completely the crackles problem (only appears at 44,1Khz). That is using the same audio buffer length (512 samples), in Tiger or Leopard, in standalone or AU mode. In a host such as Logic, the playback frequency can be set through the File->Project settings->audio menu (Options button in standalone PLAY).

As explained here and at Apple support page about latency under Logic, setting the frequency higher leads to a lower latency (duration). In fact the audio buffer length (in samples count) remains the same, but each samples is shorter (in duration) due to the higher playback frequency rate. We could also read an interesting article at Sound on Sound stating that the audio buffer length isn’t the sole parameter to consider in the latency management. Setting the frequency higher puts more load to the CPU, but not that much from 44,1 to 48Khz, and the better latency achieved seems to have fixed the crackles problem in MOR (that is with the Echo MIA audio card and its current core audio driver version).
These tests tend to confirm that the MOR DVDs weren’t defective.


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