asio_format.h

Design notes

Functions 8

• fninline bool formatIsSupported(long type)
  Whether this build converts that format at all.
  asio::formatIsSupported · asio_format.h:52
• fninline size_t formatBytes(long type)
  How many bytes one sample of that format occupies in a driver buffer.
  asio::formatBytes · asio_format.h:59
• fninline float formatScale(long type)
  The full-scale magnitude of the integer formats.
  More

  The Lsb16/18/20/24 variants are the awkward ones: a 32-bit container holding a smaller word, RIGHT-aligned. An interface that reports kAsioInt32Lsb24 wants 24 bits of range in a 32-bit slot, and writing 32 bits into it is 256x too loud -- which is not distortion, it is a number that wraps every few samples.

  asio::formatScale · asio_format.h:77
• fninline void writeSamples(void* destination, long type, const float* source, size_t stride, size_t frames)
  A run of float samples into a driver buffer: frames of them, read stride floats apart from source (2 for one side of interleaved stereo), written to frames 0..frames-1 of destination in the driver's format.
  More

  Clamped before conversion, not after. A sample above full scale wraps to the opposite sign when it is truncated into an integer, and a wrap is a full-scale click rather than the clipping a listener would forgive.

  The scale is (max + 1) and the written value uses (max), so +1.0 lands on the largest representable positive rather than one past it. The asymmetry is real and is in every fixed-point audio format: there is one more negative code than positive.

  A RUN, because that is what the buffer switch converts: two channels each way, a block each. It went through writeSample one sample at a time, which picked the format again for every sample and kept nothing in a register from one to the next: 1.6 to 1.9 ns a sample, seven times what the standalone spends on a whole 256-frame block around a DSP that does nothing. Here the format is picked once and each loop is that format's arithmetic alone. writeSample is a run of one, so this is still the only copy of each conversion.

  asio::writeSamples · asio_format.h:128
• fninline void readSamples(const void* source, long type, float* destination, size_t stride, size_t frames)
  The exact inverse, a run at a time: frames 0..frames-1 of a driver buffer out as floats, written stride apart into destination. A format this build does not convert reads as silence, not garbage.
  asio::readSamples · asio_format.h:176
• fninline void writeSample(void* destination, size_t i, long type, float v)
  One float sample into a driver buffer, at frame i: a run of one (see writeSamples, for the clamp and the scale).
  asio::writeSample · asio_format.h:224
• fninline float readSample(const void* source, size_t i, long type)
  The exact inverse: one sample of a driver buffer back out as a float.
  asio::readSample · asio_format.h:229
• fninline long hostMessageReply(long selector, long value, bool* wantsReset)
  What a host answers to the driver's asioMessage(selector, value).
  More

  wantsReset is set when the driver asked for the stream to be rebuilt -- the caller tears down and reopens on its own thread, never inside this callback, which may arrive on the driver's.

  • ResetRequest: supported. The driver will not apply its change until we reopen it, so saying yes and doing nothing is what hangs a control panel.
  • BufferSizeChange: NOT supported, on purpose. Answering 0 is what the interface specifies for a host that cannot resize live, and a driver that gets it falls back to ResetRequest -- the path we do support.
  • ResyncRequest: acknowledged. It invalidates the driver's timestamps, and nothing here reads them.
  • LatenciesChanged: acknowledged; latencies are asked for when needed, never cached.
  • SupportsTimeInfo / TimeCode: no. We register bufferSwitch, not bufferSwitchTimeInfo, and saying yes would make the driver call the null one.
  asio::hostMessageReply · asio_format.h:278

Constants 17

• constkAsioInt16Lsb = 16
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt16Lsb · asio_format.h:40
• constkAsioInt24Lsb = 17
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt24Lsb · asio_format.h:41
• constkAsioInt32Lsb = 18
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt32Lsb · asio_format.h:42
• constkAsioFloat32Lsb = 19
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioFloat32Lsb · asio_format.h:43
• constkAsioFloat64Lsb = 20
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioFloat64Lsb · asio_format.h:44
• constkAsioInt32Lsb16 = 21
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt32Lsb16 · asio_format.h:45
• constkAsioInt32Lsb18 = 22
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt32Lsb18 · asio_format.h:46
• constkAsioInt32Lsb20 = 23
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt32Lsb20 · asio_format.h:47
• constkAsioInt32Lsb24 = 24
  The sample formats a driver may hand back.
  More

  Only the little-endian ones that exist on real hardware are named. A big endian ASIO driver is a PowerPC-era Mac artefact, and float64 is in the specification but not on any interface you can buy; both are refused BY NAME in formatIsSupported rather than converted wrongly, because a wrong conversion is audible and an honest refusal is not.

  asio::kAsioInt32Lsb24 · asio_format.h:48
• constkAsioSelectorSupported = 1asio::kAsioSelectorSupported · asio_format.h:248
• constkAsioEngineVersion = 2asio::kAsioEngineVersion · asio_format.h:249
• constkAsioResetRequest = 3asio::kAsioResetRequest · asio_format.h:250
• constkAsioBufferSizeChange = 4asio::kAsioBufferSizeChange · asio_format.h:251
• constkAsioResyncRequest = 5asio::kAsioResyncRequest · asio_format.h:252
• constkAsioLatenciesChanged = 6asio::kAsioLatenciesChanged · asio_format.h:253
• constkAsioSupportsTimeInfo = 7asio::kAsioSupportsTimeInfo · asio_format.h:254
• constkAsioSupportsTimeCode = 8asio::kAsioSupportsTimeCode · asio_format.h:255