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The digital output noise at a shorted analog input randomly shows 2 values corresponding to a 16 bit representation. Accordingly, the PCM1861EVM noise floor is limited to -93 dB re full scale. However, the PCM1861 actually supports 24 bits and according to the spec's has a significantly lower noise floor. Is above observation correct? If so, is there a way to avoid the PCM1861EVM truncating the samples to 16 bits?
Thanks in advance
Hi,
We ran some tests on the PCM1861-EVM here in our lab and we see 24-bit output as expected.
As far as the results on your end is concerned, one plausible explanation is you may have wrong device on the EVM...for ex: PCM1860. Would you be able to confirm the marking on the device on the EVM that you are running the tests on? NOTE that the PCM186x family of devices share the same EVM and there is a very small change that the marking on the EVM is wrong and you may have PCM1860 instead of PCM1861.
Please do let me know if that's the case...
Best regards,
Ravi
Hi Ravi,
Thanks for your reply.
I checked the marking and it is PCM1861 on the chip as well as on the board.
Triggered by your answer, I rechecked the EVM using other software and recorded both channels 1L and 1R (nothing connected and recording at 32 bit float resolution setting). Both channels show the same quantized yet mutually uncorrelated noise of 2 distinct levels: 0 and -3.059E-5 re FS, and a noise floor of -93 dB re full scale sine. The I2S clock frequencies are 12.288 MHz, 48000 Hz and 3.072 MHz, as expected, and monitoring the DOUT line against the LRCK line, 24 bits are active indeed (the lowest of which are flipping).
Kind regards,
Jan
In addition to my previous information, I used a USB device viewer to produce the attached file showing how the EVM presents itself to the USB port.
[Port1] : USB Composite Device
---===>Device Information<===---
English product name: "USB-AudioEVM"
ConnectionStatus:
Current Config Value: 0x01 -> Device Bus Speed: Full
Device Address: 0x0F
Open Pipes: 2
===>Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x05
bEndpointAddress: 0x83 -> Direction: IN - EndpointID: 3
bmAttributes: 0x03 -> Interrupt Transfer Type
wMaxPacketSize: 0x0040 = 0x40 bytes
bInterval: 0x0A
===>Endpoint Descriptor<===
bLength: 0x09
bDescriptorType: 0x05
bEndpointAddress: 0x82 -> Direction: IN - EndpointID: 2
bmAttributes: 0x0D -> Isochronous Transfer Type
Synchronization Type = Synchronous
Bulk Transfer Type
wMaxPacketSize: 0x00C0 = 0xC0 bytes
wInterval: 0x0001
bSyncAddress: 0x00
===>Device Descriptor<===
bLength: 0x12
bDescriptorType: 0x01
bcdUSB: 0x0110
bDeviceClass: 0x00 -> This is an Interface Class Defined Device
bDeviceSubClass: 0x00
bDeviceProtocol: 0x00
bMaxPacketSize0: 0x20 = (32) Bytes
idVendor: 0x0451 = Texas Instruments
idProduct: 0xBB02
bcdDevice: 0x0304
iManufacturer: 0x01
English (United States) "TI"
iProduct: 0x02
English (United States) "USB-AudioEVM"
iSerialNumber: 0x00
bNumConfigurations: 0x01
===>Configuration Descriptor<===
bLength: 0x09
bDescriptorType: 0x02
wTotalLength: 0x00C7 -> Validated
bNumInterfaces: 0x04
bConfigurationValue: 0x01
iConfiguration: 0x00
bmAttributes: 0x80 -> Bus Powered
MaxPower: 0x32 = 100 mA
===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x00
bAlternateSetting: 0x00
bNumEndpoints: 0x00
bInterfaceClass: 0x01 -> Audio Interface Class
bInterfaceSubClass: 0x01 -> Audio Control Interface SubClass
bInterfaceProtocol: 0x00
CAUTION: This may be an invalid bInterfaceProtocol
iInterface: 0x00
===>Audio Control Interface Header Descriptor<===
bLength: 0x0A
bDescriptorType: 0x24
bDescriptorSubtype: 0x01
bcdADC: 0x0100
wTotalLength: 0x0034
bInCollection: 0x02
baInterfaceNr[1]: 0x01
baInterfaceNr[2]: 0x02
===>Audio Control Input Terminal Descriptor<===
bLength: 0x0C
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bTerminalID: 0x01
wTerminalType: 0x0101 (USB streaming)
bAssocTerminal: 0x02
bNrChannels: 0x02
wChannelConfig: 0x0003
iChannelNames: 0x00
iTerminal: 0x00
===>Audio Control Output Terminal Descriptor<===
bLength: 0x09
bDescriptorType: 0x24
bDescriptorSubtype: 0x03
bTerminalID: 0x02
wTerminalType: 0x0603 (Line connector)
bAssocTerminal: 0x01
bSourceID: 0x01
iTerminal: 0x00
===>Audio Control Input Terminal Descriptor<===
bLength: 0x0C
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bTerminalID: 0x03
wTerminalType: 0x0603 (Line connector)
bAssocTerminal: 0x04
bNrChannels: 0x02
wChannelConfig: 0x0003
iChannelNames: 0x00
iTerminal: 0x00
===>Audio Control Output Terminal Descriptor<===
bLength: 0x09
bDescriptorType: 0x24
bDescriptorSubtype: 0x03
bTerminalID: 0x04
wTerminalType: 0x0101 (USB streaming)
bAssocTerminal: 0x03
bSourceID: 0x03
iTerminal: 0x00
===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x01
bAlternateSetting: 0x00
bNumEndpoints: 0x00
bInterfaceClass: 0x01 -> Audio Interface Class
bInterfaceSubClass: 0x02 -> Audio Streaming Interface SubClass
bInterfaceProtocol: 0x00
CAUTION: This may be an invalid bInterfaceProtocol
iInterface: 0x00
===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x01
bAlternateSetting: 0x01
bNumEndpoints: 0x01
bInterfaceClass: 0x01 -> Audio Interface Class
bInterfaceSubClass: 0x02 -> Audio Streaming Interface SubClass
bInterfaceProtocol: 0x00
CAUTION: This may be an invalid bInterfaceProtocol
iInterface: 0x00
===>Audio Streaming Class Specific Interface Descriptor<===
bLength: 0x07
bDescriptorType: 0x24
bDescriptorSubtype: 0x01
bTerminalLink: 0x01
bDelay: 0x01
wFormatTag: 0x0001 (PCM)
===>Audio Streaming Format Type Descriptor<===
bLength: 0x0B
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bFormatType: 0x01
bNrChannels: 0x02
bSubframeSize: 0x02
bBitResolution: 0x10
bSamFreqType: 0x01
tSamFreq[1]: 0x00BB80 (48000 Hz)
===>Endpoint Descriptor<===
bLength: 0x09
bDescriptorType: 0x05
bEndpointAddress: 0x01 -> Direction: OUT - EndpointID: 1
bmAttributes: 0x0D -> Isochronous Transfer Type
Synchronization Type = Synchronous
Bulk Transfer Type
wMaxPacketSize: 0x00C0 = 0xC0 bytes
wInterval: 0x0001
bSyncAddress: 0x00
===>Audio Streaming Class Specific Audio Data Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x25
bDescriptorSubtype: 0x01
bmAttributes: 0x01
bLockDelayUnits: 0x00
wLockDelay: 0x0000
===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x02
bAlternateSetting: 0x00
bNumEndpoints: 0x00
bInterfaceClass: 0x01 -> Audio Interface Class
bInterfaceSubClass: 0x02 -> Audio Streaming Interface SubClass
bInterfaceProtocol: 0x00
CAUTION: This may be an invalid bInterfaceProtocol
iInterface: 0x00
===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x02
bAlternateSetting: 0x01
bNumEndpoints: 0x01
bInterfaceClass: 0x01 -> Audio Interface Class
bInterfaceSubClass: 0x02 -> Audio Streaming Interface SubClass
bInterfaceProtocol: 0x00
CAUTION: This may be an invalid bInterfaceProtocol
iInterface: 0x00
===>Audio Streaming Class Specific Interface Descriptor<===
bLength: 0x07
bDescriptorType: 0x24
bDescriptorSubtype: 0x01
bTerminalLink: 0x04
bDelay: 0x01
wFormatTag: 0x0001 (PCM)
===>Audio Streaming Format Type Descriptor<===
bLength: 0x0B
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bFormatType: 0x01
bNrChannels: 0x02
bSubframeSize: 0x02
bBitResolution: 0x10
bSamFreqType: 0x01
tSamFreq[1]: 0x00BB80 (48000 Hz)
===>Endpoint Descriptor<===
bLength: 0x09
bDescriptorType: 0x05
bEndpointAddress: 0x82 -> Direction: IN - EndpointID: 2
bmAttributes: 0x0D -> Isochronous Transfer Type
Synchronization Type = Synchronous
Bulk Transfer Type
wMaxPacketSize: 0x00C0 = 0xC0 bytes
wInterval: 0x0001
bSyncAddress: 0x00
===>Audio Streaming Class Specific Audio Data Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x25
bDescriptorSubtype: 0x01
bmAttributes: 0x01
bLockDelayUnits: 0x00
wLockDelay: 0x0000
===>Interface Descriptor<===
bLength: 0x09
bDescriptorType: 0x04
bInterfaceNumber: 0x03
bAlternateSetting: 0x00
bNumEndpoints: 0x01
bInterfaceClass: 0x03 -> HID Interface Class
bInterfaceSubClass: 0x00
bInterfaceProtocol: 0x00
CAUTION: This may be an invalid bInterfaceProtocol
iInterface: 0x00
===>HID Descriptor<===
bLength: 0x09
bDescriptorType: 0x21
bcdHID: 0x0100
bCountryCode: 0x00
bNumDescriptors: 0x01
bDescriptorType: 0x22
wDescriptorLength: 0x0022
===>Endpoint Descriptor<===
bLength: 0x07
bDescriptorType: 0x05
bEndpointAddress: 0x83 -> Direction: IN - EndpointID: 3
bmAttributes: 0x03 -> Interrupt Transfer Type
wMaxPacketSize: 0x0040 = 0x40 bytes
bInterval: 0x0A