Analog vs digital volume control - case study with Mytek Stereo192-DSD DAC
There has been a lot of discussion about different types of volume controls. For comparison purposes of one case I chose to use Mytek Stereo192-DSD DAC which has three different volume control modes; analog, digital and bypass. Signal routing is implemented using relays. DAC chip is ESS Sabre ES9016S in stereo mode (4 DACs in parallel per channel). ESS Sabre has 32-bit volume control and internal DSP pipeline so it has 8 bits more resolution than allowed by 24-bit external input. It also has higher output level than typical for increased dynamic range. I believe analog volume control chip is TI PGA2311, although the markings on the chip have been removed.
DAC was connected to iMac using Apple's Thunderbolt-to-Firewire adapter which also limits input resolution to 24-bit. Measurements were performed from the balanced outputs using typical 3 meter long XLR microphone cable (matches the typical DAC-to-power-amp case). For software volume control case
For built-in volume control, three levels were tested; -10, -60 and -96 dBFS. With software control it was possible to also use -120 dBFS setting. Source file is 44.1 kHz 32-bit PCM.
TPDF output dither for 24-bit target was used for testing built-in volume control case.
Results for the analog volume control.
-10 dBFS volume setting:
[ATTACH=CONFIG]21702[/ATTACH]
-60 dBFS volume setting:
[ATTACH=CONFIG]21703[/ATTACH]
-96 dBFS volume setting:
[ATTACH=CONFIG]21704[/ATTACH]
Results for the digital volume control.
-10 dBFS volume setting:
[ATTACH=CONFIG]21705[/ATTACH]
-60 dBFS volume setting:
[ATTACH=CONFIG]21706[/ATTACH]
-96 dBFS volume setting:
[ATTACH=CONFIG]21707[/ATTACH]
Results for DSD128 input and external software digital volume.
-10 dBFS volume setting:
[ATTACH=CONFIG]21708[/ATTACH]
-60 dBFS volume setting:
[ATTACH=CONFIG]21709[/ATTACH]
-96 dBFS volume setting:
[ATTACH=CONFIG]21710[/ATTACH]
-120 dBFS volume setting:
[ATTACH=CONFIG]21711[/ATTACH]
Results for 192/24 PCM input and external software digital volume with TPDF dither.
-60 dBFS volume setting:
[ATTACH=CONFIG]21712[/ATTACH]
-120 dBFS volume setting:
[ATTACH=CONFIG]21713[/ATTACH]
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