This article addresses the common issue encountered when using PyAudio with a Hermes Audio Server, specifically the `OSError: [Errno -9997] Invalid sample rate` error that arises when attempting to use a 16kHz sample rate while a 44.1kHz rate works flawlessly. We'll explore the underlying causes of this problem, delve into potential solutions, and offer a comprehensive troubleshooting guide. The problem, while seemingly simple, often stems from a complex interplay between PyAudio, the underlying audio system (often ALSA on Linux-based systems like the Raspberry Pi), and the Hermes Audio Server's capabilities and configuration.
Understanding the Error:
The `OSError: [Errno -9997] Invalid sample rate` error indicates that PyAudio, acting as the intermediary between your Python script and the audio hardware, is unable to set the desired sample rate of 16kHz. The `-9997` error code is specific to PyAudio and doesn't directly translate to a standard POSIX errno. It essentially signals a mismatch between the requested sample rate and what the audio system or Hermes Audio Server can support. This mismatch can arise from several sources:
* Hardware Limitations: Your audio hardware might not inherently support 16kHz sampling. While many modern devices support a wide range of sample rates, older or less capable hardware might have limitations. This is particularly relevant for embedded systems like the Raspberry Pi, where audio hardware capabilities are often more constrained.
* Driver Issues: The audio drivers (e.g., ALSA on Linux) might not be properly configured to handle 16kHz. Incorrect driver settings, outdated drivers, or conflicts with other audio applications can prevent PyAudio from successfully setting the desired sample rate.
* Hermes Audio Server Configuration: The Hermes Audio Server itself might have limitations on the sample rates it accepts. It might be configured to only accept specific sample rates, excluding 16kHz. This is crucial to investigate, as the server acts as a crucial link in the audio chain.
* PyAudio Configuration: While less common, a misconfiguration within your PyAudio setup could contribute to the problem. This could involve incorrect parameters passed to the PyAudio stream object or issues with the audio device selection.
* Conflicting Applications: Other applications accessing the audio hardware concurrently might interfere with PyAudio's attempt to set the 16kHz sample rate. This is a frequent problem on shared audio systems.
Troubleshooting Steps:
Let's systematically investigate and address the potential causes:
1. Verify Hardware Support:
* Consult Hardware Specifications: Check the specifications of your audio hardware (sound card, USB audio interface, etc.) to determine the supported sample rates. The documentation should explicitly list the range of acceptable sample rates.
* Test with Different Hardware: If possible, try using a different audio device to rule out hardware-specific limitations. This helps isolate whether the problem lies with the hardware itself or the software configuration.
2. Investigate ALSA (Linux Systems):
* Check ALSA Configuration: On Linux systems, ALSA (Advanced Linux Sound Architecture) is the primary audio subsystem. You can use the `alsamixer` command to check the current audio settings and ensure that no conflicting configurations exist. Look for settings related to sample rate and ensure they are appropriately configured.
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