Dear Mr. Brockhouse:

I really enjoyed your thorough November 1, 2019, review of the NAD C 658 on SoundStage! Simplifi. I have what may be a dumb question about playing files from an iPhone through the unit.

You note that one can play files from an iPhone or other Apple device using a software update that accesses Apple AirPlay. I understand that one also can access the music files and streaming apps on an iPhone through a Bluetooth connection (although I don’t know if iOS has aptX capability). In either case, will the stream from the iPhone be using the DAC in the iPhone or the presumably superior DAC in the NAD unit? Is there a way to be sure that it runs through the NAD’s DAC?

I realize that the iPhone generally will have AAC, and that won’t compete with the quality of the streams from, say, Tidal. However, I do have a lot of music in the iPhone that may not be readily available elsewhere. It would be helpful to know if it would be possible to eke out a bit more quality with the better DAC in the NAD.

I suppose I could buy a separate DAC and run that into the NAD’s inputs. However, after paying $1600 for the DAC in the NAD, that doesn’t seem like a very elegant or cost-efficient approach.

Thanks much,
John Geracimos
United States

Hello John:

Thanks for your letter. These are all good questions.

First thing: the NAD C 658 supports Apple AirPlay 2 out of the box. There’s no need for a software update.

As you correctly observe, you can use either AirPlay or Bluetooth to stream music from an iPhone or iPad. That can be music stored on the device, or music from an app, such as Tidal. The advantage of AirPlay over Bluetooth is that it works over Wi-Fi, and sends uncompressed CD-resolution audio. Bluetooth, on the other hand, uses lossy compression -- Apple devices support the standard Bluetooth SBC codec, as well as Bluetooth AAC (but not aptX or aptX HD). Especially when streaming uncompressed or lossless music (this could be Apple Lossless files on your device, or audio from lossless streaming services like Amazon Music HD, Qobuz, and Tidal), AirPlay will sound better.

But for high-rez streaming services like Amazon Music HD, Qobuz, and Tidal, it’s preferable to use the BluOS app, rather than streaming from your i-device via AirPlay. BluOS supports high-rez audio to 24-bit/192kHz PCM, as well as MQA. With AirPlay, you’re limited to 16/44.1 PCM.

You mention that a lot of the music on your iPhone is encoded in AAC. I assume this is music you’ve downloaded from the iTunes store, and/or music that you’ve ripped using the iTunes app using AAC compression. Even with this music, AirPlay will work better than Bluetooth -- even though the C 658 supports Bluetooth AAC, as there are losses in sound quality (reduced HF response, additional noise) when transmitting AAC files via Bluetooth AAC. That won’t happen with AirPlay. Also, AirPlay has greater range than Bluetooth -- because AirPlay uses Wi-Fi, you can stream to the C 658 from anywhere in your home where there’s a good Wi-Fi signal.

There is no need to buy a separate DAC and connect it to the C 658’s inputs. With both Bluetooth and AirPlay, your i-device will be sending digital audio, which will be converted to analog by the DAC inside the C 658.

As you correctly note, connecting an external DAC to the C 658’s analog inputs would be inelegant and wasteful. It would also be pointless if you wished to use the C 658’s Dirac Live room-correction feature, which works in the digital domain. By default, analog signals are converted to digital, and then converted back to analog at the output stage.

The C 658 has an Analog Bypass function, which is enabled in the Settings menu. You’d select this function if you were connecting an external DAC to one of the C 658’s analog inputs, otherwise the signal would go through a D-to-A conversion in the external DAC, and then A-to-D and D-to-A conversions inside the C 658. With Analog Bypass enabled, Dirac room correction would not work on any component connected to the analog input. Bottom line -- there’s no point at all in using an external DAC with the C 658.

Kindest regards,
Gordon Brockhouse