DDRC-24 installation: between pre-pro, or in tape monitor loop?

[MarkS]

I'm thinking of getting a DDRC-24 for its Dirac capabilities for my 2.0 system. I use a 10-year-old Marantz receiver with all-analog sources (CD player, newly acquired Audioengine B-Fi streamer, receiver's radio tuner, record player that I almost never use). This receiver includes 2 tape loops, so I would have the option of installing the DDRC-24 in a loop, rather than between the pre and power amps (the receiver has pre-out main-in capability), which is what the minidsp diagrams show. (But modern equipment doesn't have tape loops!)

My intuition is that the tape loop is "better" because then the DDRC would be getting full-amplitude analog signals, rather than a volume-reduced signal from the preamp, due to possible low level noise.

Is this correct? Or does it not matter?

Thanks!

 

[AnalogSteph]

As you surmised, this approach would make things a whole lot less critical in terms of noise, especially since it puts the DSP before the main volume control. You would never hear any of it if you don't really crank up the volume.

However, since I wouldn't be sure that the DDRC-24's 2 Vrms max input level reliably covers CD player output (potentially around 2.3 Vrms plus 1-2 dB worth of intersample-over peaks), I would make sure to select the 4 Vrms input option instead. You can no doubt add 2 dB of digital gain inside the DSP if need be. That would get you to a bit under 0 dBFS out worst-case and a dynamic range of about 95 dB ref. 2 Vrms in for the entire DSP end-to-end (rather than the maximum of about 100 dB).

That's by no means earth-shattering or state of the art, especially since you still need to subtract any headroom needed for EQ boost, but it should definitely be fine in practice.

Actually, you know what? The DDRC-24 has a Toslink input. You could buy a Toslink switch to connect both your CD player and streamer, bypassing the ADC stage entirely (along with the receiver's input switching). Even if you assign 2 dB of attenuation for this input just in case, that would still give you about 101 dB of output dynamic range to start with. A solid 6 dB less noise is nothing to sneeze at, not to mention that I trust the digital filters in cheap ADCs a whole lot less than in cheap DACs (this unit apparently uses an AK4626A codec - passband ripple ADC +/-0.04 dB, DAC +/-0.02 dB, both no great shakes but the DAC is definitely the less problematic one).
Plus, radio tuners and phonopres tend to have output levels well under 2 Vrms peak, so the DSP's input stage could be set up for 2 Vrms again.

I don't know how easy switching between inputs is in the DSP, but it's definitely worth a shot I say.

 

[MarkS]

Thanks for the reply! I'm going to have to decide how to go with this. I hadn't thought of a Toslink switch, that's a good idea! And converting radio isn't really necessary since the stations I listen to all have streams ...