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In Reply to: RE: Interesting! Thanks!... posted by John Elison on October 23, 2014 at 10:29:06
This is an interesting point you raise. As you noted, the white noise response is not a true representation of the actual transducer response. I should actually be establishing the transfer function with respect to the input signal. However,the difficulty is in getting an accurate transfer function for the RIAA stage and also knowing for certain that the cutting process is truly uniform in order to know for sure that I have the actual transducer response. The other limitation is in the duration of the test tone to have a sufficiently large number of occurrences for each frequency component. Given these limitations, I use the white noise response a little differently - I have a chosen reference response and map differences of other cartridges back to the reference.
I do also have the CBS STR-100 test disc, but haven't been motivated to use this as my present method seems to give me the result that I'm after which is a mapping relationship.
The observation you made regarding the attenuation characteristic mainly applies below 1kHz and is dependent on the number of points chosen for the FFT as well as LF resonances due to arm/plinth and cantilever suspension interactions. I admit that I haven't been particularly consistent in the number of points chosen for my screenshots. Beyond 1kHz, the response is reasonably representative of the transducer response - I attach a trace for my AT-OC9 which I think you will agree is essentially uniform above 1kHz. This is my reference response for mid to HF uniformity - although I use iZotope RX for my main processing, like you, I use Soundforge to zoom in and get more accurate amplitude information to plot out relative amplitude. I then use the relative differences to digitally equalise my recordings (FIR to achieve linear phase) from all other (MM) cartridges to match the OC9 response. Generally I only need to apply EQ above 8kHz and I have been very pleased with the accuracy of the results which successfully minimise the tonal differences due to frequency response variations. Of course detail retrieval etc is still highly dependent on stylus profile/condition and arm matching, so one can still "hear" a better design. I still believe that the dominant effect on sound quality is related to stylus profile and alignment in the cantilever (laterally as well as SRA) combined with cantilever materials and the accuracy of the tracking angle more than the transducer principle. I guess that's pretty much a cartridge as a whole isn't it? ;)
Incidentally, I note that you mention your new recording capability with DSD - what is your new ADC? I'm still using a Benchmark ADC1-USB which is limited to 24/96 through USB. However, I have actually settled on 24/88.2 for two reasons; The first was technical, I eliminated problems with dropped samples and glitches (even using ASIO and a fast SSD), the second was a subjective improvement in SRC when down converting to 16/44.1 for creating CDs that my mother could enjoy. Good as iZotope's SRC is, I still feel that integer downsampling is preferable subjectively.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Follow Ups:
Hi Anthony,
I have been recording with an Alesis Masterlink for 10-years, which has a maximum resolution of 24/96. I used to have Sound Forge 7 software with a spectrum analyzer, but my computer crashed and I no longer have the Sound Forge software. Like you, I always copied LPs at 24/88 for down-sampling to 16/44 but I used 24/96 for all my measurements.
Last month I decided I needed a new digital recorder and TASCAM was offering a $200 mail-in rebate on their DA-3000 so I bought one. It can record PCM up to 24/192 and DSD up to DSD128 (5.6-MHz). I'm still learning how to use it and I need to find some computer software for mastering because the DA-3000 is strictly a recorder. I kind of miss the mastering capability of the Masterlink, but the removable memory cards in the DA-3000 makes it much easier to transfer recordings to my computer. It can record on SDHC and CF memory cards, and it accepts a USB flash drive for playback only, which allows me to play DSD files from other sources. It also has an input level control so I no longer need to normalize my recordings like I did with the Masterlink. It sounds very good, too. I've been using it for playing DSD files and I really like the sound of DSD.
Best regards,
John Elison
Hi John
Thanks for the info on the Tascam unit! It looks a well thought out design - I had been looking at options but didn't know about this one. The ability to record to a memory card is rather attractive as I'm no longer bound by interface limitations or interface driver issues.
For mastering I use iZotope RX3 advanced (as a standalone application). I also have the latest SoundForge Audio Mastering suite which combines the Sony equivalent of RX3 with Soundforge. To be honest I haven't used it except for recording and pre-processing (to remove DC offset etc) before moving to RX3 which I find gives me more control and is somewhat faster. It also comes bundled with iZotope SRC and MBIT+ dither modules plus a lite version of iZotope Ozone. Again I haven' any use for that product as I just want to clean up clicks and equalise the cartridge response. Beyond that I simply want a facsimile of the LP!
If you still have the license code for Soundforge 7, you could probably get a discount for an upgrade. Sony seem to continuously be offering discounts!
The declick algorithms in RX3 are somewhat more effective and offer slightly greater flexibility than Soundforge's native algorithm and the proprietary iZotope SRC and MBIT+ dither modules are very transparent when set "appropriately".
One warning though - RX3 does benefit greatly from a fast processor. I built a workstation around an i7-4770k and this just gives me ~2x real time when doing more advanced processing in RX3.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
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