I think perhaps this discussion could become more valuable if we
think about some of the different classes where we might need to apply this.
Since I don't DO discs, I would like to start with an analogy from
the tape world.
No, Tom, I don't connect my A-D directly to the head and do
NAB/CCIR/IEC equalization in the software. For one, you need an
integrator as well as the equalizer as the voltage output rises 6 dB
per octave off the tape head.
BUT, I do record the machine outputs and the Dolby/dbx/Telcom outputs
as TWO stereo pairs when I'm doing music work. I may not deliver the
non-decoded file, but I may. In this way, if there is ever any
question about the processing, we can do the analog re-processing
without having to replay the analog tape.
I also use the DSP to correct for using instrumentation recorders for
playing back audio, so in that sense I do add the NAB curve (or some
approximation that better matches the actual sound on the tape since
one might suspect that the recorder wasn't very accurate to begin
with). As you know, instrumentation recorders are essentially
constant current record which means that there is some playback
equalization for the thickness loss and other losses in the tape
path. The only pre-equalization is typically to adjust for
high-frequency losses in the 300 kHz - 2 MHz range, depending on tape
machine and that's only adjusted at the highest speed (60-120 in/s).
Conversely, I attempt to dial out all audio EQ when I'm reproducing
instrumentation tapes on audio recorders--but that probably
won't happen again now that my instrumentation recorder population
has increased beyond all reasonableness <sigh/smile>.
There is another use I make of DSP and that's correcting odd
off-speed replay when I need to, but, for my common off-speed replay
(like 3.75 -50% varispeed to obtain 1.88 in/s), I have a separate
preset that has been equalized to the 1.88 in/s MRL tape on the machines.
Now back to discs.
I would think that there is a time and a place to use both systems. I
would guess that there might be a good reason to use hardware RIAA EQ
(and by the way, the National Association of Broadcaster's
publication of that curve is now available as are the tape standards
at www.richardhess.com/tape/history/ ) for playback of "late model"
discs and use software for the wide variety of other EQs.
There is a movement afoot (partially pushed by TracerTek -- the
people who sell DC7 and flat preamps) that flat transfers with
digital EQ is superior. I see Chas. Lawson's similar post, but I'm
surprised analog components drift as much and as quickly as he said,
but I don't doubt it happened.
I think that dividing the discs into different groups and then
discussing each group might be more informative than lumping all
The original question was for RIAA but there are few RIAA discs that
we should be transferring, even in Canada, as the true RIAA standard
came into effect what, 55 years ago? I don't think it was adopted
immediately, was it? I recall seeing London/Decca FFRR recordings
(but maybe they were done with the RIAA curve and they just used the
acronym for marketing) into the 1960s and perhaps the 1970s.
The freeware from Australia that I pointed Scott to last night does
"delta" equalization, so it appears that you can tell it that you
used an RIAA preamp to make the transfer and then it changes RIAA to
FFRR or whatever.
Finally, when I have attempted to do RIAA playback, I have noted a
WIDE variety of apparent responses from built-in preamps in
receivers. I use an RTS-405 preamp which has adjustable R and C
cartridge loading and I first adjusted it by ear based on several LPs
and a CDs that I believed to be mastered from the same source. After
doing that I found I was within about 2 dB of the CBS test record at
12 kHz. I tweaked a little more to bring the CBS test record into
alignment. This setup is much brighter and has more detail (without
sounding bad) than most of the preamps in receivers. Of course, that
exacerbates surface noise, but, when properly adjusted there was
surprisingly little difference between the CDs and the LPs other than
the noise of the LP.
This has led me to speculate that at least one source of the critique
of CDs as "sounding harsh" comes from a combination of overly bright
speakers and rolled off RIAA preamps so that some of the disc noise
So, I think this whole area needs further discussion and narrower categories.
At 09:09 AM 2008-08-25, Tom Fine wrote:
>OK Charles, I'll take the bait ;) ...
>What DSP RIAA "decoder" do you recommend? Do you also do this for
>tapes (ie take a flat feed at either head levels or no-EQ amplified
>level and decode in the computer)?
>-- Tom Fine
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.